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: 2, 4, and 5.

- Some of the potential energy of the feather is converted into kinetic energy. (The feather gains speed as it falls, so part of its gravitational PE becomes KE.)
- Some of the rocks’ potential energy is converted into thermal energy due to the friction of air resistance. (Rocks experience some air drag and also produce heat/sound/deformation on impact, so not literally all PE becomes KE.)
- Some of the feather’s potential energy is converted into thermal energy due to the friction of air resistance. (Air resistance does significant work on the feather, turning part of its PE into thermal energy.)

The statements saying “all” of the rocks’ or feather’s PE is converted into a single form are incorrect because both bodies experience multiple energy transfers (KE plus some thermal/sound/deformation losses), and wind resistance is not zero.