1.
Work....
Correct Answer
A. Changes the amount of mechanical energy an object has.
Explanation
This answer is correct because work is defined as the transfer of energy to or from an object, resulting in a change in its mechanical energy. It can either increase or decrease the amount of mechanical energy an object possesses. This can happen through various means such as applying a force, lifting an object against gravity, or transferring energy between different forms (kinetic to potential or vice versa). Work is not limited to only affecting the speed of an object or being caused by friction.
2.
An object has mechanical energy. This object could.... (CHECK ALL THAT APPLY!)
Correct Answer(s)
A. ...have kinetic energy
B. ...have potential energy
C. ...have both kinetic and potential energy.
Explanation
An object with mechanical energy can have kinetic energy if it is in motion, potential energy if it is at a position where it can potentially move due to gravity or other forces, or both kinetic and potential energy if it is both in motion and at a position where it can potentially move. It is not necessary for the object to be at rest on the ground to have mechanical energy.
3.
A car hits a patch of ice while going downhill. All of it's potential energy turns into kinetic energy. Assume there is no friction and you can neglect air resistance. In this situation, the car is experiencing:
Correct Answer
C. Conservation of Mechanical Energy
Explanation
In this situation, the car is experiencing Conservation of Mechanical Energy. Conservation of Mechanical Energy states that the total amount of mechanical energy in a system remains constant as long as no external forces are acting on it. In this case, the car's potential energy due to its position on the hill is converted into kinetic energy as it starts moving downhill. Since there is no friction or air resistance, no external forces are acting on the car, and therefore the total mechanical energy of the car remains constant throughout the process.
4.
A trick pilot puts her plane into a nosedive. All of the plane's potential energy turns into kinetic energy. Assume there is no friction and you can neglect air resistance. In this situation, the plane is experiencing:
Correct Answer
C. Conservation of Mechanical Energy
Explanation
When the trick pilot puts her plane into a nosedive, the potential energy of the plane is converted into kinetic energy. This means that the total mechanical energy of the plane remains constant. Conservation of Mechanical Energy states that in the absence of external forces like friction or air resistance, the total mechanical energy of a system remains constant. Therefore, the correct answer is Conservation of Mechanical Energy.
5.
You lift a box over your head at a constant velocity. In this situation, the box is experiencing:
Correct Answer
A. Positive Work
Explanation
When you lift a box over your head at a constant velocity, the box is experiencing positive work. This is because work is defined as the product of the force applied on an object and the displacement of the object in the direction of the force. In this case, you are applying an upward force on the box, and the displacement of the box is also in the upward direction. Therefore, the work done on the box is positive.
6.
A child drags a sled up a hill. In this situation, the sled is experiencing:
Correct Answer
A. Positive Work
Explanation
When a child drags a sled up a hill, the sled is moving in the same direction as the applied force. According to the definition of work, work is done when a force is applied to an object and the object moves in the direction of the force. Therefore, the sled is experiencing positive work.
7.
A large man is sliding down a slip-n-slide when he hits the grass and comes quickly to a stop In this situation, the man is experiencing:
Correct Answer
B. Negative Work
Explanation
In this situation, the man is experiencing negative work. Negative work occurs when the force applied on an object is in the opposite direction of its displacement. As the man slides down the slip-n-slide, the force of friction between his body and the slide is acting in the opposite direction of his motion, causing him to slow down and eventually come to a stop on the grass. This means that the work done by the frictional force is negative, as it is acting against the direction of motion.
8.
A futuristic astronaut is floating, still and abandoned, in space. Then an alien tractor beam locks on to her and accelerates her forward. She is experiencing:
Correct Answer
A. Positive Work
Explanation
The astronaut is experiencing positive work because the alien tractor beam is applying a force on her in the direction of her motion, causing her to accelerate forward. Work is defined as the product of the force applied on an object and the displacement of the object in the direction of the force. In this case, the force applied by the tractor beam is in the same direction as the displacement of the astronaut, resulting in positive work being done on her.
9.
The brakes of a car are applied. In this situation, the car is experiencing:
Correct Answer
B. Negative Work
Explanation
When the brakes of a car are applied, the car comes to a stop or slows down. In this situation, the force applied by the brakes is opposite to the direction of motion of the car. As a result, the work done by the brakes is negative because work is defined as the product of force and displacement in the direction of the force. Therefore, the correct answer is negative work.
10.
Your friend is sitting in a shopping car. You rush up and push the cart forward. Your friend's mechanical energy...
Correct Answer
A. Increased
Explanation
When you push the shopping cart forward, you are adding kinetic energy to the system. This increase in kinetic energy results in an increase in your friend's mechanical energy. Therefore, the correct answer is "Increased."
11.
Your crush comes flying toward you on the ice skating rink, out of control. You grab on to them and bring them to a stop. Your crush's mechanical energy...
Correct Answer
B. Decreased
Explanation
When you grab your crush and bring them to a stop, you are exerting a force on them to reduce their kinetic energy. As a result, their mechanical energy, which is the sum of their kinetic and potential energy, decreases. Therefore, the correct answer is decreased.
12.
You accelerate the motorcycle you are riding by giving it a little gas. Your mechanical energy...
Correct Answer
A. Increased
Explanation
When you give the motorcycle a little gas, you are adding energy to the system. This increases the mechanical energy of the motorcycle. The gas provides fuel for the engine, which converts it into kinetic energy, increasing the speed and therefore the mechanical energy of the motorcycle.
13.
Mechanical energy is made of:
Correct Answer
A. Potential and kinetic energy
Explanation
Mechanical energy is the sum of potential energy and kinetic energy. Potential energy is the energy stored in an object due to its position or condition, while kinetic energy is the energy possessed by an object due to its motion. Therefore, mechanical energy is composed of both potential and kinetic energy.
14.
An object's mechanical energy increased. That means...
Correct Answer
B. Positive work was done on the object
Explanation
When an object's mechanical energy increases, it means that work has been done on the object. In this case, the correct answer is "Positive work was done on the object." This means that an external force acted on the object in the direction of its displacement, resulting in an increase in its mechanical energy.
15.
A child is resting on a sled. Then her big brother pulls her forward, doing 200 J of work. The ground is level. Friction isn't slowing the girl down. What is the girl's final kinetic energy?
Correct Answer
B. 200 J
Explanation
When the girl's big brother pulls her forward, he does 200 J of work on her. According to the work-energy principle, the work done on an object is equal to the change in its kinetic energy. Since there is no friction slowing the girl down and the ground is level, the work done by the brother increases the girl's kinetic energy by 200 J. Therefore, the girl's final kinetic energy is 200 J.
16.
A child is resting on a sled. Then her big brother pulls her forward, doing 200 J of work. Meanwhile, friction does -50 J of work on the sled. The ground is level. What is the girl's final kinetic energy?
Correct Answer
B. 150 J
Explanation
The girl's final kinetic energy can be determined by subtracting the work done by friction from the work done by her brother. The work done by her brother is 200 J, and the work done by friction is -50 J (negative because it opposes the motion). Therefore, the girl's final kinetic energy is 200 J - (-50 J) = 250 J. However, since the question asks for the girl's final kinetic energy, we need to consider that the work done by friction is negative, indicating that it reduces the girl's kinetic energy. Therefore, the correct answer is 200 J - 50 J = 150 J.
17.
A child is resting on a sled. Then her big brother pulls her forward, doing 200 J of work. Meanwhile, friction does -50 J of work on the sled. The ground is level. The girl has a mass of 35 kg. What is her final velocity?
Correct Answer
C. 2.93 m/s
Explanation
The work done by the big brother pulling the sled is positive because he is applying a force in the direction of motion, which increases the kinetic energy of the sled and the girl. The work done by friction is negative because it acts in the opposite direction of motion, reducing the kinetic energy. The net work done on the sled is the sum of the work done by the big brother and the work done by friction. The net work is equal to the change in kinetic energy, which can be calculated using the equation: net work = (1/2)mv^2 - (1/2)mv_initial^2. Solving for the final velocity, we find that it is approximately 2.93 m/s.
18.
You apply 80 J of work to a ball, throwing it straight up in the air. Assume there is no air resistance. At apogee, the ball will have...
Correct Answer
D. 80 J of potential energy, 80 J of mechanical energy
Explanation
When you throw the ball straight up in the air, it gains potential energy due to its increased height. This potential energy is equal to the amount of work done on the ball, which in this case is 80 J. Therefore, the ball will have 80 J of potential energy at apogee. Additionally, mechanical energy is the sum of kinetic energy and potential energy. Since the ball is at its highest point and has come to a stop, its kinetic energy is 0 J. However, it still has potential energy, so the ball will have 80 J of mechanical energy at apogee.
19.
You do 300 J of work on a box as you lift it from the floor up to a shelf. The box has a mass of 20 kg. The box now has...
Correct Answer
B. 300 J of potential energy
Explanation
When you lift the box from the floor up to the shelf, you do work on it against the force of gravity. This work is equal to the change in potential energy of the box. Since the work done is 300 J, the box gains 300 J of potential energy. Therefore, the correct answer is 300 J of potential energy.
20.
You do 300 J of work on a box as you lift it from the floor up to a shelf. The box has a mass of 20 kg. How high did you lift the box?
Correct Answer
D. 1.53 m
Explanation
The work done on an object is equal to the force applied multiplied by the distance over which the force is applied. In this case, the work done is 300 J. The force applied can be calculated using the formula F = m * g, where m is the mass of the box (20 kg) and g is the acceleration due to gravity (approximately 9.8 m/s^2). So, the force applied is 20 kg * 9.8 m/s^2 = 196 N. To find the distance, we can rearrange the formula for work to solve for distance: distance = work / force = 300 J / 196 N ≈ 1.53 m. Therefore, you lifted the box approximately 1.53 m.