Question

A rock falls from the top of a hill to the bottom. The total energy of the rock at the top isn’t the same as the sum of its potential energy and kinetic energy at the bottom which state meant best explains this situation
A) some of the rocks energy is transformed to thermal energy
B) the rolling rock loses some of its energy because of gravity
C) the rolling rock doesn’t follow the law of conservation of energy
D) the rock absorbs some of its own potential energy

Answer 1

Answer:

A) some of the rocks energy is transformed to thermal energy

Explanation:

If we neglect air resistance during the fall of the rock, than the mechanical energy of the rock (which is sum of its potential energy and its kinetic energy) would be constant during the entire motion, so the total energy of the rock at the top would be the same as the sum of its potential energy and kinetic energy at the bottom.

However, this not occurs, due to the presence of air resistance. In fact, air resistance acts against the fall of the rock, and because of the friction between the molecules of air and the surface of the rock, the rock loses part of its energy. This energy is converted into thermal energy of the molecules of the air.