Middle School Science Quiz: Explain Kinetic Energy Changes

What this quiz covers

This quiz focuses on Explain Kinetic Energy Changes, giving you a quick way to practice the rules, question types, and explanations that matter most for Middle School Science.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. The net force is opposite the motion (friction), so the net work is negative and the book's kinetic energy decreases. (correct answer)
2. The net force is zero, so the book's kinetic energy must decrease to zero.
3. Friction does positive work on the book, so the book loses kinetic energy.
4. The book stops because its kinetic energy turns directly into gravitational potential energy on a level table.

Question 2

1. The book's kinetic energy decreases because friction does negative work, converting kinetic energy into thermal energy in the surfaces. (correct answer)
2. The book's kinetic energy decreases because friction does positive work and speeds the book up.
3. The book's kinetic energy decreases because its mass is being used up as it slides.
4. The book's kinetic energy decreases even though no forces act on it; objects naturally slow down on their own.

Question 3

1. It increases while the student is pushing, because the applied force does positive work on the cart and increases its speed. (correct answer)
2. It increases after the student stops pushing, because friction does positive work and speeds the cart up.
3. It increases during both parts, because any force (even friction) always increases kinetic energy.
4. It never increases, because kinetic energy cannot change unless the cart's mass changes.

Question 4

1. The car's kinetic energy increases because the engine does positive work on the car by applying a forward force over a distance, which increases the car's speed. (correct answer)
2. The car's kinetic energy increases because friction from the road adds energy to the car's motion.
3. The car's kinetic energy increases even though its speed changes, because kinetic energy does not depend on speed.
4. The car's kinetic energy increases because the engine force points backward while the car moves forward, so the engine does negative work.

Question 5

1. The kinetic energy increases, so the net work must be positive.
2. The kinetic energy decreases, so the net work must be negative.
3. The kinetic energy stays constant, so the net work is zero (the forward pull is balanced by friction/drag). (correct answer)
4. The kinetic energy stays constant, but the net work must be positive because a force is applied.

Question 6

1. Because gravity acts opposite the ball's upward motion and does negative work, converting kinetic energy into gravitational potential energy. (correct answer)
2. Because gravity pushes upward while the ball rises, doing positive work and removing kinetic energy.
3. Because kinetic energy depends only on height, and the ball's height increases.
4. Because no forces act on the ball after it leaves the hand, so its kinetic energy must drop to zero.

Question 7

1. It increases because the pull force does positive work, so kinetic energy must increase even at constant speed.
2. It decreases because friction always reduces kinetic energy, even if the speed is constant.
3. It stays constant because the net force is zero, so the net work is zero and the speed (and $KE$) stays the same. (correct answer)
4. It stays constant because the box's mass is changing in a way that keeps $\tfrac{1}{2}mv^2$ the same.

Question 8

1. The ball's kinetic energy decreases because gravity does negative work on the ball while it moves upward, so kinetic energy is converted into gravitational potential energy. (correct answer)
2. The ball's kinetic energy decreases because gravity does positive work on the ball while it moves upward, adding kinetic energy.
3. The ball's kinetic energy decreases because its mass decreases as it goes higher.
4. The ball's kinetic energy stays constant because the force of gravity is perpendicular to the ball's motion on the way up.

Question 9

1. The cart's kinetic energy increases because the student's forward force does positive work on the cart, increasing its speed. (correct answer)
2. The cart's kinetic energy increases because the student's force is forward, but forward forces always do negative work.
3. The cart's kinetic energy stays constant because pushing only changes direction, not speed.
4. The cart's kinetic energy increases because friction pushes it forward and adds energy.

Question 10

1. The car's kinetic energy increases because the engine does positive work on the car (forward force over forward distance), increasing the car's speed. (correct answer)
2. The car's kinetic energy increases because friction from the road always adds energy to moving objects.
3. The car's kinetic energy stays the same because kinetic energy does not depend on speed.
4. The car's kinetic energy increases because gravity pulls down on the car, which always increases speed on level ground.

Question 11

1. It decreases because any moving object must lose kinetic energy over time, even without forces.
2. It stays constant because there is (approximately) no net force doing work on the puck, so its speed and $KE$ stay the same. (correct answer)
3. It increases because the puck is moving, so it keeps gaining kinetic energy automatically.
4. It changes because kinetic energy depends on direction, and the puck's direction could change without forces.

Question 12

1. It decreases because gravity always does negative work on moving objects.
2. It increases because the skateboarder is moving forward, so kinetic energy must increase with time.
3. It stays constant because the speed is constant, so $KE=\tfrac12 mv^2$ does not change (no net work changes the speed). (correct answer)
4. It stays constant because friction is the only force acting, and friction does zero work.

Question 13

1. The kinetic energy is larger on the way up because the ball is moving upward against gravity.
2. The kinetic energy is larger on the way down because gravity adds extra energy that wasn't there before.
3. The kinetic energy is the same at both moments because at the same height the speed is the same (energy shifts between KE and gravitational potential energy). (correct answer)
4. The kinetic energy is zero at both moments because the ball is 2 m above the ground.

Question 14

1. It stays the same, because energy is conserved and kinetic energy cannot change during a collision.
2. It increases, because the pillow pushes back on the car and adds kinetic energy.
3. It decreases, mostly converting into thermal energy, sound, and deformation of the pillow and car. (correct answer)
4. It decreases, mostly converting into gravitational potential energy because the car is lower after the collision.

Question 15

1. The cart's kinetic energy increases because the student's forward force does positive work on the cart, increasing its speed. (correct answer)
2. The cart's kinetic energy increases because the student's force is perpendicular to the motion, so it does the most work.
3. The cart's kinetic energy stays constant because any applied force is canceled by motion.
4. The cart's kinetic energy increases because the cart's mass increases as it moves faster.

Question 16

1. Its kinetic energy increases because it keeps moving forward.
2. Its kinetic energy decreases because motion always fades with time, even if speed is constant.
3. Its kinetic energy stays constant because its speed is constant, meaning net work on it is zero (no change in kinetic energy). (correct answer)
4. Its kinetic energy stays constant because friction is doing positive work that exactly adds energy.

Question 17

1. Gravity does positive work on the ball as it rises, so the ball's kinetic energy increases.
2. Gravity acts opposite the ball's motion on the way up and does negative work, converting kinetic energy into gravitational potential energy. (correct answer)
3. The ball's mass decreases as it rises, so its kinetic energy decreases.
4. No forces act on the ball after it leaves the hand, so its kinetic energy must decrease on its own.

Question 18

1. It decreases because any moving object must lose kinetic energy over time, even if its speed is constant.
2. It stays constant because the speed is constant, so $KE=\tfrac{1}{2}mv^2$ does not change and the net work is zero. (correct answer)
3. It increases because moving at constant speed means the bicycle is accelerating.
4. It stays constant because friction does positive work that exactly increases kinetic energy.

Question 19

1. The net work on the crate is zero, so the crate's kinetic energy stays constant. (correct answer)
2. The student's work is negative, so the crate's kinetic energy increases.
3. Friction does positive work, so the crate's kinetic energy stays constant.
4. Because the crate moves, the net work must be positive and kinetic energy must increase.

Question 20

1. The forward pulling force does positive work over a distance, so the wagon's kinetic energy increases as its speed increases. (correct answer)
2. The forward pulling force does negative work, so the wagon's kinetic energy increases as its speed increases.
3. The wagon's kinetic energy increases because the net force is zero, which makes objects speed up.
4. The wagon's kinetic energy increases because energy is created as it moves, without any work being done.