Question

A bird flies off of a cliff, dropping a feather and knocking rocks off the cliff. The rocks reach the ground much faster than the feather.

Which energy transformations occur in this case? Check all that apply.

All of the rocks’ potential energy is converted into kinetic energy because rocks do not experience wind resistance.
Some of the potential energy of the feather is converted into kinetic energy.
All of the feather’s potential energy is converted into thermal energy due to the friction of air resistance.
Some of the rocks’ potential energy is converted into thermal energy due to the friction of air resistance.
Some of the feather’s potential energy is converted into thermal energy due to the friction of air resistance

Answer 1

Correct choices:
- Some of the potential energy of the feather is converted into kinetic energy.
- Some of the rocks’ potential energy is converted into thermal energy due to the friction of air resistance.
- Some of the feather’s potential energy is converted into thermal energy due to the friction of air resistance.

Why: Both rock and feather lose gravitational potential energy as they fall. Part of that becomes kinetic energy. Because of air resistance (drag) some energy is dissipated as thermal (and a little sound). The rocks have much less drag so most of their PE becomes KE, but not all. The feather experiences strong drag so a significant fraction of its PE is converted to thermal; it still has some KE while falling. The two statements that say “all” of a body’s PE is converted (for rocks or feather) are incorrect.