# Quiz #5: Work, Power And Energy

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• 1.

### If a mass is at rest, what must be applied to cause it to move?

• A.

Kilograms

• B.

Speed

• C.

Vectors

• D.

Force

D. Force
Explanation
To cause a mass at rest to move, a force must be applied. Force is a push or pull that can change the state of motion of an object. In this case, the force is needed to overcome the inertia of the mass and initiate its movement. Without the application of force, the mass will remain at rest due to Newton's first law of motion.

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• 2.

### If you push on a wall with a force of 30 N, then ______________.

• A.

The wall pushes on you with a force of 30 N.

• B.

The wall moves back 3 cm.

• C.

The wall cannot be forced.

• D.

You are pulled towards the wall.

A. The wall pushes on you with a force of 30 N.
Explanation
When you push on a wall with a force of 30 N, according to Newton's third law of motion, the wall will push back on you with an equal force of 30 N. This is because for every action, there is an equal and opposite reaction. Therefore, the correct answer is that the wall pushes on you with a force of 30 N.

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• 3.

### If you have to push a car forward, what are the forces acting on you?

• A.

The car pushes back on you, gravity pulls you down, the ground pushes up on you, and friction on your shoes pushes forward on you.

• B.

Only gravity.

• C.

Your own muscles push you down.

• D.

No forces act on you.

A. The car pushes back on you, gravity pulls you down, the ground pushes up on you, and friction on your shoes pushes forward on you.
Explanation
When you push a car forward, there are multiple forces acting on you. The car pushes back on you with an equal and opposite force according to Newton's third law of motion. Gravity pulls you down towards the ground. The ground pushes up on you with a normal force to counteract gravity. Additionally, the friction between your shoes and the ground provides a forward force that helps you push the car. Therefore, the correct answer is that the car pushes back on you, gravity pulls you down, the ground pushes up on you, and friction on your shoes pushes forward on you.

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• 4.

### A person jumps to the ground from a platform 10 feet high.  Which of the following is true?

• A.

The person has more kinetic energy before they jump than after they jump.

• B.

The person has less potential energy at the top of the platform than in the air.

• C.

The person's potential energy at the instant they jump is approximately equal to their kinetic energy the instant they land.

• D.

The person's kinetic energy at the instant they jump is approximately double their potential energy the instant they land.

C. The person's potential energy at the instant they jump is approximately equal to their kinetic energy the instant they land.
Explanation
When the person is at the top of the platform, they have maximum potential energy due to their height. As they jump, their potential energy decreases and is converted into kinetic energy, which is the energy of motion. At the instant they jump, their potential energy is equal to their kinetic energy because all the potential energy has been converted into kinetic energy. When they land on the ground, their kinetic energy is at its maximum as they are moving with the highest velocity, while their potential energy is zero because they are at ground level. Therefore, the person's potential energy at the instant they jump is approximately equal to their kinetic energy the instant they land.

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• 5.

### The potential energy of an object is equal to ____________.

• A.

The work done on the object to put the object into its current state.

• B.

The velocity of the object divided by its mass.

• C.

The force of gravity working on the object.

• D.

The size of the object compared to its surface area.

A. The work done on the object to put the object into its current state.
Explanation
The potential energy of an object is determined by the work done on the object to bring it into its current state. This means that the potential energy is a result of the energy transferred to the object when work is done on it. The work done can be due to factors such as lifting the object against gravity or compressing a spring. Therefore, the correct answer is "the work done on the object to put the object into its current state."

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• 6.

### The kinetic energy of an object will increase the most if you __________________.

• A.

Double the velocity of the object

• B.

Double the mass of the object

• C.

Double the potential energy

• D.

Double the temperature of the object

A. Double the velocity of the object
Explanation
The kinetic energy of an object is directly proportional to the square of its velocity. Therefore, doubling the velocity of the object will result in the greatest increase in its kinetic energy. This is because the kinetic energy formula, K = 1/2 mv^2, shows that the velocity has a greater impact on the kinetic energy than mass, potential energy, or temperature.

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• 7.

### "Power" is defined as _________________.

• A.

The rate at which work is done

• B.

The energy necessary to do work

• C.

The velocity of an object squared

• D.

The sum of potential and kinetic energy

A. The rate at which work is done
Explanation
The correct answer is "the rate at which work is done." Power is a measure of how quickly work is being done or how fast energy is being transferred. It is the amount of work done per unit of time. Power is not the energy itself or the velocity of an object squared. It is also not the sum of potential and kinetic energy, as that would be the total mechanical energy.

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• 8.

### An object with mass "m" kilograms is suspended "h" meters above the ground by a string.  If the string is cut, what will the velocity of the object be at the instant it hits the ground?

• A.

The square root of 2gh

• B.

One-half the mass squared

• C.

Two times ghm squared

• D.

H-2gm

A. The square root of 2gh
Explanation
When the string is cut, the object will fall freely due to gravity. According to the laws of physics, the velocity of a falling object can be calculated using the equation v = sqrt(2gh), where "v" is the velocity, "g" is the acceleration due to gravity, and "h" is the height from which the object falls. Therefore, the correct answer is the square root of 2gh.

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• 9.

### Which of the following is NOT a consequence of "The Law of Conservation of Energy"?

• A.

Potential Energy can never be greater than Kinetic Energy

• B.

The energy in a closed system is always constant

• C.

The Kinetic Energy of a dropped object at the instant it hits the ground is roughly equal to the potential energy of the object at the instant it was dropped

• D.

It is not necessary to use Kinematics to discover the velocity of an object accelerated by gravity if you know it's initial Potential Energy and its mass.

A. Potential Energy can never be greater than Kinetic Energy
Explanation
The Law of Conservation of Energy states that energy cannot be created or destroyed, only transferred or transformed. It does not dictate that potential energy cannot be greater than kinetic energy. In fact, in many situations, potential energy can be greater than kinetic energy. For example, when an object is thrown upwards, it has more potential energy at its highest point than kinetic energy. Therefore, the statement "Potential Energy can never be greater than Kinetic Energy" is not a consequence of the Law of Conservation of Energy.

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• 10.

### As an object goes up a hill at constant velocity, which of the following is NOT true?

• A.

The object's Potential Energy is increasing.

• B.

The object's Kinetic Energy is decreasing.

• C.

The object's Kinetic Energy is constant.

• D.

The object's speed is constant.

B. The object's Kinetic Energy is decreasing.
Explanation
As an object goes up a hill at constant velocity, its potential energy is increasing because it is gaining height. However, its kinetic energy remains constant because its speed is not changing. The object's speed is also constant because it is moving at a constant velocity. Therefore, the statement "The object's kinetic energy is decreasing" is not true.

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• Current Version
• Mar 22, 2023
Quiz Edited by
ProProfs Editorial Team
• Oct 03, 2011
Quiz Created by
Mcdonellm1

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