Question

1. a boy holds a ball of clay above the floor. he drops the clay ball, and it speeds up as it falls to the floor. the clay ball flattens as it hits the floor and remains flat. when the clay ball hits the floor, the clay and the floor get a little warmer. (assume that no energy is transferred between the clay ball and the air or between the floor and the air.) as the clay ball falls and hits the floor, does the total amount of energy in the system (the clay ball and the floor) increase, decrease, or stay the same? why? a. the total amount of energy in the system increases because the clay ball and the floor are warmer, and therefore, have more energy. b. the total amount of energy in the system decreases. although the energy of the clay ball and the floor increases as they get warmer, the energy of the clay ball decreases by an even greater amount as it moves closer to the ground. c. the total amount of energy in the system stays the same because the decrease in energy due to the clay ball moving closer to the ground is equal to the increase in energy due to the clay ball and floor getting warmer. d. the total amount of energy in the system stays the same. even though the clay ball and the floor are warmer, being warmer is not associated with the amount of energy an object has.

Explanation:

According to the law of conservation of energy, energy cannot be created or destroyed, only transformed. In this system (clay ball and floor), as the clay ball falls, its gravitational potential energy is converted into kinetic energy. When it hits the floor, the kinetic energy is converted into thermal energy (making the clay and floor warmer) and other forms like deformation energy (flattening). The total energy in the system remains the same because the decrease in gravitational potential energy (as the ball moves closer to the ground) is equal to the increase in thermal and deformation energy (as they get warmer and the ball flattens).

• Option A is wrong because energy is not created, the warmth is just a form of energy transformation, not an increase in total energy.
• Option B is wrong because energy is not destroyed, the total energy should stay the same.
• Option D is wrong because being warmer (increase in thermal energy) is associated with the amount of energy an object has.

Answer:

C. The total amount of energy in the system stays the same because the decrease in energy due to the clay ball moving closer to the ground is equal to the increase in energy due to the clay ball and floor getting warmer.