Energy Types: Compare and Contrast KE & PE

A ball is held at the top of a hill and then released. As it rolls down, describe how the energy transformation occurs and explain which point along the path has the greatest kinetic energy and why.

• The ball has the most kinetic energy at the top because it has the most potential energy stored there.

• The ball has the most kinetic energy at the bottom because all the gravitational potential energy has been converted to kinetic energy.

• The ball has equal kinetic energy at all points because energy is always constant.

• The ball has the most kinetic energy halfway down because that is where the transformation begins.

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A stretched rubber band and a moving car both possess energy. Using your understanding of potential and kinetic energy, explain which object has elastic potential energy and which has kinetic energy, and justify your reasoning.

• Both the rubber band and the car have kinetic energy because they are both capable of doing work.

• The car has elastic potential energy and the rubber band has kinetic energy because the car is larger.

• The rubber band has elastic potential energy due to its stretched position, and the moving car has kinetic energy due to its motion.

• Both the rubber band and the car have potential energy because neither is in its final resting state.

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A student claims that a book sitting on a high shelf and a compressed spring have the same type of potential energy. Evaluate this claim and explain whether it is correct or incorrect using evidence.

• The student is correct because both objects are not moving, so they both have the same type of potential energy.

• The student is incorrect because the book has gravitational potential energy due to its height, while the compressed spring has elastic potential energy due to its deformation.

• The student is correct because all forms of potential energy are identical regardless of the source.

• The student is incorrect because the book has kinetic energy and the spring has chemical potential energy.

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Two identical balls are placed at different heights on a ramp. Ball A is placed at 10 meters high and Ball B is placed at 5 meters high. Using reasoning about gravitational potential energy and kinetic energy, predict which ball will be moving faster when it reaches the bottom and explain why.

• Ball B will be moving faster because it has less distance to travel and loses less energy to friction.

• Both balls will move at the same speed because they have the same mass.

• Ball A will be moving faster because it has more gravitational potential energy at the top, which converts to more kinetic energy at the bottom.

• Ball A will be moving faster because heavier objects always fall faster than lighter ones.

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A skateboarder starts at the top of a half-pipe and slides down. At the bottom, she has maximum speed. She then rises up the other side and slows down. Using evidence, explain the energy transformations happening throughout this process.

• The skateboarder gains new energy from the ground as she moves, which is why she speeds up and slows down.

• Gravitational potential energy converts to kinetic energy as she descends, and kinetic energy converts back to gravitational potential energy as she ascends.

• Kinetic energy is created at the bottom and destroyed at the top, showing that energy is not conserved.

• The skateboarder's chemical potential energy converts to kinetic energy throughout the entire ride.

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A student is comparing a moving bicycle and a piece of food. She says both have energy but in different forms. Plan an explanation that identifies the type of energy in each object and justifies why they are different forms.

• Both the bicycle and the food have kinetic energy because both are capable of producing motion.

• The bicycle has chemical potential energy because it uses fuel, and the food has kinetic energy because it moves through the digestive system.

• The moving bicycle has kinetic energy due to its motion, while the food has chemical potential energy stored in its molecular bonds.

• The bicycle has gravitational potential energy because it is elevated off the ground, and the food has elastic potential energy.

A roller coaster car starts from rest at the top of a tall hill. Using reasoning about energy transformations, predict what happens to the gravitational potential energy and kinetic energy as the car descends and then climbs a smaller hill.

• Gravitational potential energy increases as the car descends and kinetic energy decreases as it climbs the smaller hill.

• Gravitational potential energy decreases as the car descends and converts to kinetic energy; as it climbs the smaller hill, kinetic energy converts back to gravitational potential energy.

• Both gravitational potential energy and kinetic energy increase throughout the entire ride.

• Kinetic energy remains constant throughout the ride because the car's mass does not change.

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A student stretches a bungee cord and releases it to launch a small toy. Using evidence, explain how elastic potential energy and kinetic energy are involved in this scenario and identify the moment when each type of energy is at its maximum.

• The toy has maximum kinetic energy when the cord is fully stretched, and maximum elastic potential energy when the toy is in mid-air.

• The elastic potential energy is at its maximum when the cord is fully stretched, and the kinetic energy is at its maximum when the cord returns to its natural length and the toy is moving fastest.

• Both elastic potential energy and kinetic energy are at their maximum at the same time when the cord is halfway stretched.

• The toy only has gravitational potential energy throughout the entire process because it is being launched upward.

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Compare the energy stored in a battery to the energy of a falling rock. Using reasoning, explain which type of potential energy each represents and how each converts to kinetic energy.

• Both the battery and the falling rock have gravitational potential energy because both are affected by gravity.

• The battery has elastic potential energy that converts to kinetic energy when used, while the falling rock has gravitational potential energy that converts to kinetic energy as it falls.

• The battery has chemical potential energy stored in its bonds that converts to kinetic energy when used in a device, while the falling rock has gravitational potential energy that converts to kinetic energy as it falls.

• The battery has kinetic energy because electricity moves through it, and the falling rock has elastic potential energy because it compresses the ground when it lands.

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A student argues that a stationary object can never have kinetic energy. Evaluate this argument and use reasoning to explain whether it is always, sometimes, or never true.

• The argument is never true because all objects, even stationary ones, have kinetic energy due to their mass.

• The argument is always true because kinetic energy depends on motion, and a stationary object has zero velocity, meaning its kinetic energy is 0.

• The argument is sometimes true because stationary objects can have kinetic energy if they are on a slope.

• The argument is always true because stationary objects only have chemical potential energy.

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