1.
All of the following require the application of a net force, except?
Correct Answer
B. To maintain an object in motion at a constant velocity
Explanation
The application of a net force is not required to maintain an object in motion at a constant velocity. According to Newton's first law of motion, an object will continue to move at a constant velocity unless acted upon by an external force. Therefore, if an object is already in motion at a constant velocity, no additional net force is needed to keep it moving at that same velocity.
2.
A rocket flies at constant velocity straight up. whats the direction of the net force on the rocket?
Correct Answer
E. None of the previous
Explanation
Since the rocket is flying at a constant velocity straight up, we know that the forces acting on it are balanced. If there was a net force in any direction, the rocket's velocity would change. Therefore, the direction of the net force on the rocket is none of the previous options.
3.
A hot rod starting at rest and uniformly accelerating covers a distance of 400 meters in 15 seconds. What is the acceleration to two significant figures?
Correct Answer
A. 3.6 m/s^2
Explanation
The hot rod is starting at rest and uniformly accelerating, meaning its speed is increasing at a constant rate. The distance covered by the hot rod is 400 meters and the time taken is 15 seconds. To find the acceleration, we can use the equation: acceleration = (final velocity - initial velocity) / time. Since the hot rod starts at rest, its initial velocity is 0 m/s. The final velocity can be found by dividing the distance covered by the time taken: final velocity = distance / time = 400 m / 15 s = 26.67 m/s. Plugging these values into the equation, we get: acceleration = (26.67 m/s - 0 m/s) / 15 s = 1.78 m/s^2. Rounding to two significant figures, the acceleration is 1.8 m/s^2.
4.
A ball is thrown up at 15 m/s, whats the velocity after 3.0 seconds?
Correct Answer
B. 14 m/s down
Explanation
The velocity of the ball after 3.0 seconds can be determined using the equation of motion. When the ball is thrown up, it experiences a constant acceleration due to gravity pulling it downwards. After reaching its highest point, the ball starts to fall back down. Since the velocity is measured after 3.0 seconds, the ball has already reached its highest point and is on its way back down. Therefore, the velocity after 3.0 seconds is 14 m/s downward.
5.
A 20.0 kg block on a smooth horizontal surface is acted upon by two horizontal forces: a force of 20 N acting to the left and a force of 60 N to the right? The acceleration fo the block will be
Correct Answer
E. None
6.
Which of the following units would be appropriate to describe force?
Correct Answer
A. Kg*m/s^2
Explanation
The unit kg*m/s^2, also known as Newton (N), is the appropriate unit to describe force. This is because force is defined as the product of mass (kg) and acceleration (m/s^2). Therefore, kg*m/s^2 represents the force required to accelerate a mass of 1 kilogram at a rate of 1 meter per second squared.
7.
A 0.15 kg ball traveling with a speed of 50 m/s is brought to rest in a catcher's mitt with an average force of 75 N. What is the maginutde of the impulse exerted by the mitt on the ball?
Correct Answer
D. 7.5 Ns
Explanation
When an object is brought to rest, the change in momentum is equal to the impulse exerted on it. The impulse is calculated by multiplying the average force applied to the object by the time interval over which the force is applied. In this case, the average force is 75 N and the time interval is not given. However, since the ball is brought to rest, we know that the time interval is equal to the time it takes for the ball to stop. Using the equation for acceleration, a = (final velocity - initial velocity) / time, we can rearrange it to find the time, time = (final velocity - initial velocity) / acceleration. Plugging in the values, time = (0 - 50) / (75 / 0.15) = -50 / (75 / 0.15) = -0.2 s. Since time cannot be negative, we take the absolute value and get 0.2 s. Finally, we can calculate the impulse by multiplying the average force by the time, impulse = 75 N * 0.2 s = 15 Ns. Therefore, the magnitude of the impulse exerted by the mitt on the ball is 15 Ns.
8.
A child plays on a see-saw with her father. The child has a weight of 250 N and is seated 2.5 m from the axis of rotation. Her father balances her when he is seated 0.80 m from the axis. The fathers weight is
Correct Answer
E. 750 N
Explanation
The father balances the child on the see-saw, which means that their torques must be equal. Torque is calculated by multiplying the force applied by the distance from the axis of rotation. The child's torque is 250 N * 2.5 m = 625 Nm. To balance this, the father's torque must also be 625 Nm. Since the father is seated at a distance of 0.80 m from the axis, his weight can be calculated by dividing the torque by the distance: 625 Nm / 0.80 m = 781.25 N. Rounding this to the nearest 5 N gives us the answer of 750 N.
9.
A book weighing 10 N is held at rest in the palm of the hand. The reaction to the force of the hand on the book is a force of
Correct Answer
C. 10 N exerted by the book on the hand
Explanation
When the book is held at rest in the palm of the hand, the reaction force to the force of the hand on the book is exerted by the book on the hand. This is because of Newton's third law of motion which states that for every action, there is an equal and opposite reaction. So, the book exerts a force of 10 N on the hand.
10.
A ball is projected upward with an initial velocity of 5 m/s. It will reach its maximum height in approximately
Correct Answer
A. 0.5 s
Explanation
When a ball is projected upward with an initial velocity, it will reach its maximum height when its velocity becomes zero. This happens because the ball is constantly being slowed down by the force of gravity. The time it takes for the ball to reach its maximum height is equal to the time it takes for its velocity to become zero. Therefore, the ball will reach its maximum height in approximately 0.5 seconds.
11.
If an astronaut landed on a planet that was three times the diameter and three times the mass of earth, how would his weight there compare with that on earth?
Correct Answer
D. One third as much
Explanation
The weight of the astronaut on the planet would be one third as much as his weight on Earth because weight is directly proportional to mass. Since the planet has three times the mass of Earth, the gravitational force acting on the astronaut would also be three times stronger. However, weight is also inversely proportional to the square of the distance between two objects. Since the planet has three times the diameter of Earth, the distance between the astronaut and the planet's center would also be three times greater. Therefore, the increased gravitational force would be counteracted by the increased distance, resulting in the astronaut experiencing one third of his weight on Earth.
12.
Temperature can be described as
Correct Answer
B. A measure of the average kinetic energy of the molecules of a substance
Explanation
Temperature can be described as a measure of the average kinetic energy of the molecules of a substance. This means that temperature is a measure of how fast the molecules of a substance are moving. When the molecules move faster, the temperature is higher, and when they move slower, the temperature is lower. This concept is important in understanding how heat is transferred between objects, as the movement of molecules is directly related to the transfer of energy.
13.
A positive charge is released from rest near a bar magnet. The magnetic force on the charge
Correct Answer
E. Theres no magnetic force on the charge
Explanation
The correct answer is that there is no magnetic force on the charge. This is because a positive charge does not experience a magnetic force when it is at rest near a bar magnet. Magnetic forces are only exerted on moving charges, not stationary charges. Therefore, in this scenario, the charge will not be attracted or repelled by either pole of the magnet.
14.
A current of 2.5 A is flowing through a resistance of 18 Ohms. What is the voltage difference across this resistance?
Correct Answer
C. 45 V
Explanation
The voltage difference across a resistance can be calculated using Ohm's Law, which states that voltage (V) is equal to current (I) multiplied by resistance (R). In this case, the current is given as 2.5 A and the resistance is given as 18 Ohms. By multiplying these values together (2.5 A * 18 Ohms), we find that the voltage difference across the resistance is 45 V.
15.
If you stand directly in front of a planar (flat) mirror with a distance of 3 feet between you and the mirror, your image appears
Correct Answer
D. 6 feet from you, same size
Explanation
When you stand directly in front of a planar mirror with a distance of 3 feet between you and the mirror, your image appears 6 feet from you, but the size remains the same. This is because the image in a mirror is formed by the reflection of light rays, and the distance between the object and the mirror is equal to the distance between the image and the mirror. The size of the image remains the same because the mirror reflects the light rays in a way that preserves the proportions of the object being reflected.