Answer to Question #212547 in Physics for Yang

Question

1. Two people observe a leaf falling from a tree. One person is standing on a ladder and the other is on the ground. If each person were to compare the energy of the leaf observed, would each person find the following to be the same or different for the leaf, from the point where it falls off the tree to when it hits the ground: (a) the kinetic energy of the leaf; (b) the change in gravitational potential energy; (c) the final gravitational potential energy?
2. An external force acts on a particle during a trip from one point to another and back to that same point. This particle is only affected by conservative forces. Does this particle’s kinetic energy and potential energy change as a result of this trip? Explain.
3. A child jumps up and down on a bed, reaching a higher height after each bounce. Explain how the child can increase his maximum gravitational potential energy with each bounce.

Answer 1

1. If both observers agree that they determine the potential energy related to the ground:

(a) the kinetic energy of the leaf would be the same;

(b) the change in gravitational potential energy would be the same;

(c) the final gravitational potential energy would be the same.

2. The kinetic and potential energies do not change because the forces are conservative.

3. The child can do this by resonance, or approaching the frequency of his jumps to the frequency of the rebounding bed.