Chapter 6: Work And Energy

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  • 1/82 Questions

    A 4.0-kg mass is moving with speed 2.0 m/s. A 1.0-kg mass is moving with speed 4.0 m/s. Both objects encounter the same constant braking force, and are brought to rest. Which object travels the greater distance before stopping?

    • The 4.0-kg mass
    • The 1.0-kg mass
    • Both travel the same distance.
    • Cannot be determined from the information given
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About This Quiz

Explore the fundamentals of work and energy in physics through this engaging quiz. Assess your understanding of key concepts such as the units of work, conditions for work in static scenarios, and practical applications of the work-energy principle. Ideal for students enhancing their physics knowledge.

Work And Energy Quizzes & Trivia

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  • 2. 

    Is it possible for a system to have negative potential energy?

    • Yes, as long as the total energy is positive.

    • Yes, since the choice of the zero of potential energy is arbitrary.

    • No, because the kinetic energy of a system must equal its potential energy.

    • No, because this would have no physical meaning.

    Correct Answer
    A. Yes, since the choice of the zero of potential energy is arbitrary.
    Explanation
    The correct answer is "Yes, since the choice of the zero of potential energy is arbitrary." This means that the reference point for measuring potential energy can be chosen arbitrarily, and therefore it is possible for a system to have negative potential energy depending on the chosen reference point. The total energy of the system can still be positive, even if the potential energy is negative.

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  • 3. 

    Of the following, which is not a unit of power?

    • Watt/second

    • Newton-meter/second

    • Joule/second

    • Watt

    Correct Answer
    A. Watt/second
    Explanation
    The correct answer is watt/second. This is because watt/second is not a unit of power. Power is measured in watts, which is a unit of energy transfer per unit time. The other options, newton-meter/second and joule/second, are not units of power either. Newton-meter/second is a unit of torque, and joule/second is a unit of energy transfer rate.

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  • 4. 

    Describe the energy of a car driving up a hill.

    • Entirely kinetic

    • Entirely potential

    • Both kinetic and potential

    • Gravitational

    Correct Answer
    A. Both kinetic and potential
    Explanation
    When a car is driving up a hill, it possesses both kinetic and potential energy. Kinetic energy is the energy of motion, which the car has as it moves up the hill. Potential energy is the energy that an object possesses due to its position or height above the ground. As the car gains height while driving up the hill, it gains potential energy. Therefore, the energy of a car driving up a hill is both kinetic and potential.

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  • 5. 

    A 10-N force is needed to move an object with a constant velocity of 5.0 m/s. What power must be delivered to the object by the force?

    • 0.50 W

    • 1.0 W

    • 50 W

    • 100 W

    Correct Answer
    A. 50 W
    Explanation
    The power delivered to an object is calculated by multiplying the force applied to the object by its velocity. In this case, the force applied is 10 N and the velocity is 5.0 m/s. Multiplying these values gives us 50 W, which is the power that must be delivered to the object.

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  • 6. 

    The quantity 1/2 mv^2 is

    • The kinetic energy of the object.

    • The potential energy of the object.

    • The work done on the object by the force.

    • The power supplied to the object by the force.

    Correct Answer
    A. The kinetic energy of the object.
    Explanation
    The quantity 1/2 mv^2 represents the kinetic energy of an object. Kinetic energy is the energy possessed by an object due to its motion. It is dependent on the mass of the object (m) and the square of its velocity (v^2). The formula 1/2 mv^2 is derived from the work-energy theorem, which states that the work done on an object is equal to the change in its kinetic energy. Therefore, the correct answer is the kinetic energy of the object.

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  • 7. 

    If the net work done on an object is negative, then the object's kinetic energy

    • Decreases.

    • Remains the same.

    • Increases.

    • Is zero.

    Correct Answer
    A. Decreases.
    Explanation
    When the net work done on an object is negative, it means that the work done on the object is in the opposite direction of its motion. This implies that the object is losing energy, resulting in a decrease in its kinetic energy. Therefore, the correct answer is that the object's kinetic energy decreases.

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  • 8. 

    If the net work done on an object is zero, then the object's kinetic energy

    • Decreases.

    • Remains the same.

    • Increases.

    • Is zero.

    Correct Answer
    A. Remains the same.
    Explanation
    If the net work done on an object is zero, it means that the total amount of work done on the object is equal to zero. This implies that there is no change in the object's kinetic energy. Therefore, the object's kinetic energy remains the same.

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  • 9. 

    Compared to yesterday, you did 3 times the work in one-third the time. To do so, your power output must have been

    • The same as yesterday's power output.

    • One-third of yesterday's power output.

    • 3 times yesterday's power output.

    • 9 times yesterday's power output.

    Correct Answer
    A. 9 times yesterday's power output.
    Explanation
    If you did 3 times the work in one-third the time compared to yesterday, it means that your power output increased. To do 3 times the work in one-third the time, you would need to exert 9 times more power than yesterday.

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  • 10. 

    The kinetic friction force between a 60.0-kg object and a horizontal surface is 50.0 N. If the initial speed of the object is 25.0 m/s, what distance will it slide before coming to a stop?

    • 15.0 m

    • 30.0 m

    • 375 m

    • 750 m

    Correct Answer
    A. 375 m
    Explanation
    The kinetic friction force between the object and the horizontal surface is 50.0 N. This force opposes the motion of the object and causes it to slow down. The frictional force is directly proportional to the normal force, which is equal to the weight of the object in this case. Therefore, the frictional force can be calculated using the equation Ff = μ * Fn, where μ is the coefficient of kinetic friction. Since the mass of the object is given as 60.0 kg, we can calculate the normal force as Fn = m * g, where g is the acceleration due to gravity. By rearranging the equation, we can solve for the coefficient of kinetic friction, which turns out to be 50.0 N / (60.0 kg * 9.8 m/s^2) = 0.085. Using the equation Ff = μ * Fn, we can now calculate the force of friction as 0.085 * (60.0 kg * 9.8 m/s^2) = 50.0 N. The force of friction can also be expressed as Ff = m * a, where a is the acceleration of the object. Rearranging the equation, we can solve for the acceleration as a = Ff / m = 50.0 N / 60.0 kg = 0.833 m/s^2. The final speed of the object is 0 m/s since it comes to a stop. Using the equation v^2 = u^2 + 2as, where v is the final speed, u is the initial speed, a is the acceleration, and s is the distance, we can solve for the distance as s = (v^2 - u^2) / (2a) = (0^2 - 25.0 m/s^2) / (2 * 0.833 m/s^2) = 375 m. Therefore, the object will slide a distance of 375 m before coming to a stop.

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  • 11. 

    A 60-kg skier starts from rest from the top of a 50-m high slope. What is the speed of the slier on reaching the bottom of the slope? (Neglect friction.)

    • 22 m/s

    • 31 m/s

    • 9.8 m/s

    • 41 m/s

    Correct Answer
    A. 31 m/s
    Explanation
    The skier starts from rest at the top of the slope, so the initial velocity is 0 m/s. The skier will experience a change in height of 50 m as they go down the slope. Using the equation v^2 = u^2 + 2as, where v is the final velocity, u is the initial velocity, a is the acceleration, and s is the displacement, we can solve for the final velocity. Since the acceleration due to gravity is constant and equal to 9.8 m/s^2, and the displacement is -50 m (negative because the skier is moving downward), we have v^2 = 0^2 + 2(-9.8)(-50). Solving for v, we get v = 31 m/s.

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  • 12. 

    A 1500-kg car accelerates from 0 to 25 m/s in 7.0 s. What is the average power delivered by the engine? (1 hp = 746 W)

    • 60 hp

    • 70 hp

    • 80 hp

    • 90 hp

    Correct Answer
    A. 90 hp
    Explanation
    The average power delivered by the engine can be calculated using the formula: Power = Work/Time. In this case, the work done is equal to the change in kinetic energy, which can be calculated using the formula: Work = (1/2)mv^2, where m is the mass of the car and v is the final velocity. The time is given as 7.0 s. By substituting the values into the formulas, we can find the average power delivered by the engine.

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  • 13. 

    An object hits a wall and bounces back with half of its original speed. What is the ratio of the final kinetic energy to the initial kinetic energy?

    • 1/2

    • 1/4

    • 2

    • 4

    Correct Answer
    A. 1/4
    Explanation
    When an object hits a wall and bounces back with half of its original speed, its final kinetic energy is proportional to the square of its final speed. Since the final speed is half of the initial speed, the final kinetic energy will be one-fourth (1/4) of the initial kinetic energy. Therefore, the ratio of the final kinetic energy to the initial kinetic energy is 1/4.

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  • 14. 

    An object is lifted vertically 2.0 m and held there. If the object weighs 90 N, how much work was done in lifting it?

    • 360 J

    • 180 J

    • 90 J

    • 0 J

    Correct Answer
    A. 180 J
    Explanation
    When an object is lifted vertically, work is done against the force of gravity. The work done is equal to the force applied multiplied by the distance over which the force is applied. In this case, the object weighs 90 N and is lifted vertically 2.0 m. Therefore, the work done in lifting the object is 90 N * 2.0 m = 180 J.

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  • 15. 

    A 4.00-kg box of fruit slides 8.0 m down a ramp, inclined at 30.0° from the horizontal. If the box slides at a constant velocity of 5.00 m/s, what is the work done by the weight of the box?

    • 157 J

    • -157 J + 78.4 J

    • 78.4 J

    • -78.4 J

    Correct Answer
    A. 157 J
    Explanation
    The work done by the weight of the box can be calculated using the formula: work = force x distance x cos(angle). In this case, the force is the weight of the box, which can be calculated using the formula: weight = mass x gravity. The distance is given as 8.0 m and the angle is 30.0 degrees. Plugging in the values, we can calculate the work done by the weight of the box to be 157 J.

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  • 16. 

    A projectile of mass m leaves the ground with a kinetic energy of 220 J. At the highest point in its trajectory, its kinetic energy is 120 J. To what vertical height, relative to its launch point, did it rise?

    • 220/(mg) meters

    • 120/(mg) meters

    • 100/(mg) meters

    • Impossible to determine without knowing the angle of launch

    Correct Answer
    A. 100/(mg) meters
    Explanation
    The correct answer is 100/(mg) meters. This can be determined by using the principle of conservation of energy. At the highest point in its trajectory, the projectile's kinetic energy is equal to zero, and all of its initial kinetic energy is converted into potential energy. Therefore, the change in potential energy is equal to the initial kinetic energy. Using the formula for potential energy, which is mgh, where m is the mass, g is the acceleration due to gravity, and h is the vertical height, we can set up the equation 220 J = mgh. Solving for h, we get h = 220/(mg) meters. Similarly, at the highest point, the kinetic energy is 120 J, so we can set up the equation 120 J = mgh and solve for h to get h = 120/(mg) meters. Therefore, the projectile rose to a vertical height of 100/(mg) meters.

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  • 17. 

    How many joules of energy are used by a 1.0 hp motor that runs for 1.0 hr? (1 hp = 746 W)

    • 3.6 * 10^3 J

    • 2.7 * 10^6 J

    • 4.5 * 10^4 J

    • 4.8 J

    Correct Answer
    A. 2.7 * 10^6 J
    Explanation
    A 1.0 hp motor is equivalent to 746 W. Since the motor runs for 1.0 hr, we can calculate the energy used by multiplying the power (746 W) by the time (1.0 hr). This gives us 746 J/hr. However, we need to convert the units to joules, so we multiply by 3600 s/hr to get 2,677,600 J, which can be written in scientific notation as 2.7 * 10^6 J. Therefore, the correct answer is 2.7 * 10^6 J.

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  • 18. 

    What is the correct unit of work expressed in SI units?

    • Kg m/s^2

    • Kg m^2/s

    • Kg m^2/s^2

    • Kg^2 m/s^2

    Correct Answer
    A. Kg m^2/s^2
    Explanation
    The correct unit of work expressed in SI units is kg m^2/s^2. Work is defined as the product of force and displacement, and the SI unit for force is kg m/s^2 (also known as a Newton). Therefore, when force is multiplied by displacement (in meters), the resulting unit for work is kg m^2/s^2.

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  • 19. 

    The area under the curve, on a Force versus position (F vs. x) graph, represents

    • Work.

    • Kinetic energy.

    • Power.

    • Potential energy.

    Correct Answer
    A. Work.
    Explanation
    The area under the curve on a Force versus position graph represents work. This is because work is defined as the product of force and displacement, and the area under the curve represents the integral of force with respect to displacement. Therefore, calculating the area under the curve gives us the amount of work done.

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  • 20. 

    The quantity mgy is

    • The kinetic energy of the object.

    • The gravitational potential energy of the object.

    • The work done on the object by the force.

    • The power supplied to the object by the force.

    Correct Answer
    A. The gravitational potential energy of the object.
    Explanation
    The quantity mgy represents the product of the mass (m), the acceleration due to gravity (g), and the height (y) of the object. This equation is derived from the formula for gravitational potential energy, which is given by mgh. The only difference is that y is used instead of h to represent the height. Therefore, mgy represents the gravitational potential energy of the object.

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  • 21. 

    If the net work done on an object is positive, then the object's kinetic energy

    • Decreases.

    • Remains the same.

    • Increases.

    • Is zero.

    Correct Answer
    A. Increases.
    Explanation
    When the net work done on an object is positive, it means that the total work done on the object is in the same direction as its motion. This indicates that the object is gaining energy and its kinetic energy is increasing. Therefore, the correct answer is "increases."

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  • 22. 

    A lightweight object and a very heavy object are sliding with equal speeds along a level frictionless surface. They both slide up the same frictionless hill. Which rises to a greater height?

    • The heavy object, because it has greater kinetic energy.

    • The lightweight object, because it weighs less.

    • They both slide to the same height.

    • Cannot be determined from the information given.

    Correct Answer
    A. They both slide to the same height.
    Explanation
    The correct answer is that they both slide to the same height. Although the heavy object has greater kinetic energy, this does not affect the height it reaches on the hill. The height reached by an object sliding up a hill is determined by its initial speed and the shape of the hill, not its mass or kinetic energy. Therefore, both objects will reach the same height on the hill regardless of their weights or speeds.

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  • 23. 

    Does the centripetal force acting on an object do work on the object?

    • Yes, since a force acts and the object moves, and work is force times distance.

    • Yes, since it takes energy to turn an object.

    • No, because the object has constant speed.

    • No, because the force and the displacement of the object are perpendicular.

    Correct Answer
    A. No, because the force and the displacement of the object are perpendicular.
    Explanation
    The centripetal force acting on an object does not do work on the object because the force and the displacement of the object are perpendicular. In order for work to be done, the force and the displacement must be in the same direction. Since the centripetal force always acts towards the center of the circular motion, while the displacement is tangential to the motion, they are perpendicular to each other and no work is done.

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  • 24. 

    Car J moves twice as fast as car K, and car J has half the mass of car K. The kinetic energy of car J, compared to car K is

    • The same.

    • 2 to 1.

    • 4 to 1.

    • 1 to 2.

    Correct Answer
    A. 2 to 1.
    Explanation
    Car J moves twice as fast as car K, which means that its velocity is twice that of car K. The kinetic energy of an object is proportional to the square of its velocity. Since car J has twice the velocity of car K, its kinetic energy will be four times greater. However, car J has half the mass of car K. The kinetic energy is also proportional to the mass of the object. Since car J has half the mass of car K, its kinetic energy will be half that of car K. Therefore, the ratio of the kinetic energy of car J to car K is 2 to 1.

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  • 25. 

    A brick is moving at a speed of 3 m/s and a pebble is moving at a speed of 5 m/s. If both objects have the same kinetic energy, what is the ratio of the brick's mass to the rock's mass?

    • 25 to 9

    • 5 to 3

    • 12.5 to 4.5

    • 3 to 5

    Correct Answer
    A. 25 to 9
    Explanation
    The ratio of the brick's mass to the rock's mass is 25 to 9 because kinetic energy is directly proportional to mass. Since both objects have the same kinetic energy, the ratio of their masses will be the same as the ratio of their speeds squared. The ratio of the speeds squared is (3^2)/(5^2) = 9/25, so the ratio of the masses is 25 to 9.

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  • 26. 

    The quantity 1/2 kx^2 is

    • The kinetic energy of the object.

    • The elastic potential energy of the object.

    • The work done on the object by the force.

    • The power supplied to the object by the force.

    Correct Answer
    A. The elastic potential energy of the object.
    Explanation
    The quantity 1/2 kx^2 represents the elastic potential energy of the object. Elastic potential energy is the energy stored in a stretched or compressed object, and it is directly proportional to the square of the displacement (x) from the equilibrium position and the spring constant (k). Therefore, the given expression, 1/2 kx^2, accurately represents the elastic potential energy of the object.

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  • 27. 

    Consider two masses m(1) and m(2) at the top of two frictionless inclined planes. Both masses start from rest at the same height. However, the plane on which m(1) sits is at an angle of 30° with the horizontal, while the plane on which m(2) sits is at 60°. If the masses are released, which is going faster at the bottom of its plane?

    • M(1)

    • M(2)

    • They both are going the same speed.

    • Cannot be determined without knowing the masses.

    Correct Answer
    A. They both are going the same speed.
    Explanation
    Both masses m(1) and m(2) are released from the same height and experience the same gravitational force. The speed of an object sliding down an inclined plane depends only on the height from which it is released and not on the angle of the incline. Therefore, both masses will have the same speed at the bottom of their respective planes. The masses and angles of the inclines do not affect the speed.

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  • 28. 

    A 10-kg mass, hung onto a spring, causes the spring to stretch 2.0 cm. What is the spring constant?

    • 4.9 * 10^3 N/m

    • 5.0 * 10^3 N/m

    • 20 N/m

    • 20 N/m

    Correct Answer
    A. 4.9 * 10^3 N/m
    Explanation
    The spring constant can be calculated using Hooke's Law, which states that the force exerted by a spring is directly proportional to the displacement of the spring from its equilibrium position. The equation is given by F = -kx, where F is the force, k is the spring constant, and x is the displacement. In this case, a 10-kg mass causes the spring to stretch 2.0 cm (or 0.02 m). Using the equation, we can calculate the force exerted by the mass on the spring, which is equal to the force exerted by the spring on the mass. Rearranging the equation, we get k = -F/x. Plugging in the values, we get k = -(10 kg * 9.8 m/s^2) / 0.02 m = -490 N/m. Since the spring constant is always positive, we take the absolute value and get 490 N/m, which is equivalent to 4.9 * 10^2 N/m.

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  • 29. 

    A planet of constant mass orbits the Sun in an elliptical orbit. Neglecting any friction effects, what happens to the planet's kinetic energy?

    • It remains constant.

    • It increases continually.

    • It decreases continually.

    • It increases when the planet approaches the Sun, and decreases when it moves farther away.

    Correct Answer
    A. It increases when the planet approaches the Sun, and decreases when it moves farther away.
    Explanation
    As the planet moves closer to the Sun in its elliptical orbit, it experiences a stronger gravitational force. This increased force causes the planet to accelerate, resulting in an increase in its kinetic energy. Conversely, as the planet moves farther away from the Sun, the gravitational force weakens, causing the planet to decelerate and its kinetic energy to decrease. Therefore, the planet's kinetic energy increases when it approaches the Sun and decreases when it moves farther away.

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  • 30. 

    An object is released from rest a height h above the ground. A second object with four times the mass of the first if released from the same height. The potential energy of the second object compared to the first is

    • One-fourth as much.

    • One-half as much.

    • Twice as much.

    • Four times as much.

    Correct Answer
    A. Four times as much.
    Explanation
    When an object is released from rest, its potential energy is converted into kinetic energy as it falls. The potential energy of an object is given by the equation PE = mgh, where m is the mass, g is the acceleration due to gravity, and h is the height. In this case, the height is the same for both objects, but the mass of the second object is four times greater than the mass of the first object. Therefore, the potential energy of the second object is four times greater than the potential energy of the first object.

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  • 31. 

    The total mechanical energy of a system

    • Is equally divided between kinetic energy and potential energy.

    • Is either all kinetic energy or all potential energy, at any one instant.

    • Can never be negative.

    • Is constant, only if conservative forces act.

    Correct Answer
    A. Is constant, only if conservative forces act.
    Explanation
    The correct answer is that the total mechanical energy of a system is constant, only if conservative forces act. This means that if the only forces acting on a system are conservative forces (such as gravity or springs), then the total mechanical energy (the sum of kinetic and potential energy) will remain constant over time. Non-conservative forces, such as friction or air resistance, can convert mechanical energy into other forms (such as heat or sound), causing the total mechanical energy of the system to change.

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  • 32. 

    An acorn falls from a tree. Compare its kinetic energy K, to its potential energy U.

    • K increases and U decreases.

    • K decreases and U decreases.

    • K increases and U increases.

    • K decreases and U increases.

    Correct Answer
    A. K increases and U decreases.
    Explanation
    As the acorn falls from the tree, its potential energy is converted into kinetic energy. The potential energy of the acorn decreases as it falls closer to the ground, while its kinetic energy increases due to its motion. Therefore, the correct answer is that the kinetic energy increases and the potential energy decreases.

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  • 33. 

    A 400-N box is pushed up an inclined plane. The plane is 4.0 m long and rises 2.0 m. If the plane is frictionless, how much work was done by the push?

    • 1600 J

    • 800 J

    • 400 J

    • 100 J

    Correct Answer
    A. 800 J
    Explanation
    The work done by the push can be calculated using the formula: work = force x distance. In this case, the force is the weight of the box, which is given as 400 N. The distance is the length of the inclined plane, which is 4.0 m. Therefore, the work done is 400 N x 4.0 m = 1600 J. However, since the question asks for the work done by the push, we need to consider only the component of the force that is parallel to the direction of motion. This component can be found using trigonometry, and it is equal to the weight of the box multiplied by the cosine of the angle between the inclined plane and the horizontal. Since the plane rises 2.0 m over a length of 4.0 m, the angle can be found using the inverse tangent function: angle = arctan(2.0/4.0) = 26.57 degrees. Therefore, the work done by the push is 400 N x cos(26.57 degrees) x 4.0 m = 800 J.

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  • 34. 

    An object slides down a frictionless inclined plane. At the bottom, it has a speed of 9.80 m/s. What is the vertical height of the plane?

    • 19.6 m

    • 9.80 m

    • 4.90 m

    • 2.45 m

    Correct Answer
    A. 4.90 m
    Explanation
    The vertical height of the plane can be determined using the equation of motion for an object sliding down an inclined plane. The equation is given by v^2 = u^2 + 2as, where v is the final velocity (9.80 m/s), u is the initial velocity (0 m/s since the object starts from rest), a is the acceleration (which is equal to the acceleration due to gravity, g), and s is the vertical height of the plane. Rearranging the equation, we get s = (v^2 - u^2) / (2a). Substituting the given values, we find s = (9.80^2 - 0^2) / (2 * 9.8) = 4.90 m. Therefore, the vertical height of the plane is 4.90 m.

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  • 35. 

    The quantity Fd/t is

    • The kinetic energy of the object.

    • The potential energy of the object.

    • The work done on the object by the force.

    • The power supplied to the object by the force.

    Correct Answer
    A. The power supplied to the object by the force.
    Explanation
    The quantity Fd/t represents the power supplied to the object by the force. Power is defined as the rate at which work is done or the amount of energy transferred per unit time. In this case, F represents the force applied to the object, d represents the displacement of the object, and t represents the time taken. Therefore, Fd/t represents the power supplied to the object by the force.

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  • 36. 

    An arrow of mass 20 g is shot horizontally into a bale of hay, striking the hay with a velocity of 60 m/s. It penetrates a depth of 20 cm before stopping. What is the average stopping force acting on the arrow?

    • 45 N

    • 90 N

    • 180 N

    • 360 N

    Correct Answer
    A. 180 N
    Explanation
    When the arrow is shot into the bale of hay, it comes to a stop after penetrating a certain depth. The average stopping force acting on the arrow can be calculated using the equation F = m * a, where F is the force, m is the mass, and a is the acceleration. In this case, we know the mass of the arrow (20 g) and the velocity at which it strikes the hay (60 m/s). To find the acceleration, we can use the equation v^2 = u^2 + 2as, where v is the final velocity (0 m/s), u is the initial velocity (60 m/s), a is the acceleration, and s is the distance penetrated (20 cm = 0.2 m). Rearranging the equation, we get a = (v^2 - u^2) / (2s). Plugging in the values, we find that the acceleration is -9000 m/s^2. Multiplying this by the mass of the arrow, we get the average stopping force of 180 N.

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  • 37. 

    Can work be done on a system if there is no motion?

    • Yes, if an outside force is provided.

    • Yes, since motion is only relative.

    • No, since a system which is not moving has no energy.

    • No, because of the way work is defined.

    Correct Answer
    A. No, because of the way work is defined.
    Explanation
    Work is defined as the transfer of energy that occurs when a force is applied to an object and the object is displaced in the direction of the force. If there is no motion, there is no displacement, and therefore no work is done. Work requires both force and displacement to be present in order to be defined and calculated.

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  • 38. 

    If you push twice as hard against a stationary brick wall, the amount of work you do

    • Doubles.

    • Is cut in half.

    • Remains constant but non-zero.

    • Remains constant at zero.

    Correct Answer
    A. Remains constant at zero.
    Explanation
    When you push against a stationary brick wall, the wall does not move. In order for work to be done, there must be a displacement in the direction of the force applied. Since the wall does not move, there is no displacement and therefore no work is done. Therefore, the amount of work remains constant at zero, regardless of how hard you push.

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  • 39. 

    You throw a ball straight up. Compare the sign of the work done by gravity while the ball goes up with the sign of the work done by gravity while it goes down.

    • Work is + on the way up and + on the way down.

    • Work is + on the way up and - on the way down.

    • Work is - on the way up and + on the way down.

    • Work is - on the way up and - on the way down.

    Correct Answer
    A. Work is - on the way up and + on the way down.
    Explanation
    When the ball is thrown straight up, the work done by gravity is negative because the force of gravity is acting in the opposite direction of the displacement of the ball. As the ball comes back down, the work done by gravity is positive because the force of gravity is now acting in the same direction as the displacement of the ball. Therefore, the correct answer is that the work is - on the way up and + on the way down.

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  • 40. 

    You slam on the brakes of your car in a panic, and skid a certain distance on a straight, level road. If you had been traveling twice as fast, what distance would the car have skidded, under the same conditions?

    • It would have skidded 4 times farther.

    • It would have skidded twice as far.

    • It would have skidded 1.4 times farther.

    • It is impossible to tell from the information given.

    Correct Answer
    A. It would have skidded 4 times farther.
    Explanation
    If the car had been traveling twice as fast, it would have had twice the kinetic energy. When the brakes are applied, the car's kinetic energy is converted into heat energy through friction, causing the car to skid. Since the car has twice the initial kinetic energy, it would take four times as much energy to bring the car to a stop, resulting in the car skidding four times farther.

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  • 41. 

    A ball drops some distance and gains 30 J of kinetic energy. Do not ignore air resistance. How much gravitational potential energy did the ball lose?

    • More than 30 J

    • Exactly 30 J

    • Less than 30 J

    • Cannot be determined from the information given

    Correct Answer
    A. More than 30 J
    Explanation
    When a ball drops and gains kinetic energy, it means that it is converting gravitational potential energy into kinetic energy. Since the ball gains 30 J of kinetic energy, it must have lost more than 30 J of gravitational potential energy.

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  • 42. 

    A 15.0-kg object is moved from a height of 5.00 m above a floor to a height of 13.0 m above the floor. What is the change in gravitational potential energy?

    • Zero

    • 1030 J

    • 1176 J

    • 1910 J

    Correct Answer
    A. 1176 J
    Explanation
    The change in gravitational potential energy can be calculated using the formula: ΔPE = mgh, where ΔPE is the change in gravitational potential energy, m is the mass of the object, g is the acceleration due to gravity, and h is the change in height. In this case, the mass of the object is 15.0 kg, the acceleration due to gravity is 9.8 m/s^2, and the change in height is 13.0 m - 5.0 m = 8.0 m. Plugging these values into the formula, we get ΔPE = 15.0 kg * 9.8 m/s^2 * 8.0 m = 1176 J. Therefore, the correct answer is 1176 J.

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  • 43. 

    A driver, traveling at 22 m/s, slows down her 2000 kg car to stop for a red light. What work is done by the friction force against the wheels?

    • -2.2 * 10^4 J

    • -4.4 * 10^4 J

    • -4.84 * 10^5 J

    • -9.68 * 10^5 J

    Correct Answer
    A. -4.84 * 10^5 J
    Explanation
    When the driver slows down her car, the friction force acts in the opposite direction to the motion of the car. This means that the work done by the friction force is negative. The magnitude of the work done can be calculated using the formula W = Fd, where W is the work done, F is the force, and d is the distance. In this case, the force is the friction force and the distance is the distance traveled while slowing down to a stop. Since the work done is negative, it means that energy is being taken away from the car, which is consistent with the car slowing down. The correct answer of -4.84 * 10^5 J indicates the magnitude of the negative work done by the friction force.

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  • 44. 

    A ball drops some distance and loses 30 J of gravitational potential energy. Do not ignore air resistance. How much kinetic energy did the ball gain?

    • More than 30 J

    • Exactly 30 J

    • Less than 30 J

    • Cannot be determined from the information given

    Correct Answer
    A. Less than 30 J
    Explanation
    When a ball drops and loses gravitational potential energy, it gains an equal amount of kinetic energy according to the law of conservation of energy. Since the ball loses 30 J of gravitational potential energy, it gains 30 J of kinetic energy. Therefore, the correct answer is "exactly 30 J" and not "less than 30 J".

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  • 45. 

    A 50-N object was lifted 2.0 m vertically and is being held there. How much work is being done in holding the box in this position?

    • More than 100 J

    • 100 J

    • Less than 100 J, but more than 0 J

    • 0 J

    Correct Answer
    A. 0 J
    Explanation
    When an object is held in a stationary position, no work is being done on the object. Work is defined as the transfer of energy that occurs when a force is applied over a distance. In this case, the object is not moving vertically, so there is no displacement and therefore no work is being done. Therefore, the correct answer is 0 J.

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  • 46. 

    You lift a 10-N physics book up in the air a distance of 1.0 m, at a constant velocity of 0.50 m/s. What is the work done by the weight of the book?

    • +10 J

    • -10 J

    • +5.0 J

    • -5.0 J

    Correct Answer
    A. -10 J
    Explanation
    The work done by the weight of the book is calculated using the formula: work = force x distance x cos(theta). In this case, the force is the weight of the book, which is 10 N. The distance is 1.0 m. Since the book is being lifted upwards, the angle between the force and displacement is 180 degrees, so cos(theta) = -1. Therefore, the work done is -10 J.

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  • 47. 

    A horizontal force of 200 N is applied to move a 55-kg cart (initially at rest) across a 10 m level surface. What is the final kinetic energy of the cart?

    • 1.0 * 10^3 J

    • 2.0 * 10^3 J

    • 2.7 * 10^3 J

    • 4.0 * 10^3 J

    Correct Answer
    A. 2.0 * 10^3 J
    Explanation
    The final kinetic energy of the cart can be calculated using the formula K.E. = 1/2 * m * v^2, where m is the mass of the cart and v is the final velocity. In this case, the force applied is causing the cart to accelerate, so we need to find the final velocity first. We can use Newton's second law of motion, F = m * a, where F is the force applied, m is the mass of the cart, and a is the acceleration. Rearranging the equation, we get a = F/m. Plugging in the values, we have a = 200 N / 55 kg = 3.64 m/s^2. Now, we can use the kinematic equation v^2 = u^2 + 2as, where u is the initial velocity (which is 0 m/s since the cart is initially at rest), a is the acceleration, and s is the distance traveled. Plugging in the values, we have v^2 = 0 + 2 * 3.64 m/s^2 * 10 m = 72.8 m^2/s^2. Taking the square root of both sides, we get v = 8.53 m/s. Now, we can calculate the final kinetic energy using the formula K.E. = 1/2 * m * v^2. Plugging in the values, we have K.E. = 1/2 * 55 kg * (8.53 m/s)^2 = 2.0 * 10^3 J. Therefore, the correct answer is 2.0 * 10^3 J.

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  • 48. 

    A 1.0-kg ball falls to the floor. When it is 0.70 m above the floor, its potential energy exactly equals its kinetic energy. How fast is it moving?

    • 3.7 m/s

    • 6.9 m/s

    • 14 m/s

    • 45 m/s

    Correct Answer
    A. 3.7 m/s
    Explanation
    When the ball is 0.70 m above the floor, its potential energy is given by mgh, where m is the mass of the ball (1.0 kg), g is the acceleration due to gravity (9.8 m/s^2), and h is the height above the floor (0.70 m). Its kinetic energy is given by (1/2)mv^2, where v is the velocity of the ball. Since the potential energy equals the kinetic energy, we can equate the two equations and solve for v. By substituting the given values into the equation and solving for v, we find that the ball is moving at a speed of 3.7 m/s.

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  • 49. 

    A 500-kg elevator is pulled upward with a constant force of 5500 N for a distance of 50.0 m. What is the net work done on the elevator?

    • 2.75 * 10^5 J

    • -2.45 * 10^5 J

    • 3.00 * 10^4 J

    • -5.20 * 10^5 J

    Correct Answer
    A. 3.00 * 10^4 J
    Explanation
    The net work done on the elevator can be calculated using the formula W = F * d, where W is the work done, F is the force applied, and d is the distance traveled. In this case, the force applied is 5500 N and the distance traveled is 50.0 m. Multiplying these values together gives a net work done of 275,000 J or 2.75 * 10^5 J. Therefore, the correct answer is 2.75 * 10^5 J.

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Quiz Review Timeline (Updated): Mar 21, 2023 +

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  • Mar 21, 2023
    Quiz Edited by
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  • Sep 17, 2012
    Quiz Created by
    Drtaylor
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