A cat with mass 4.0 kg jumps down to the floor from a bookcase 2.0 m high. What is the cat's change in
gravitational potential energy?

-7J

Explanation:

To determine the change in potential energy, use the equation ΔPE=mgΔh

Δ

PE=mg

Δ

h

, where m is the mass, g= 9.8 m/s2

g= 9.8 m/s

2

, and Δh is the change in height. Hence, we have that the potential energy PE=4.0 kg×9.8 m/s2×-2.0 m=-78 J

PE=4.0 kg

×

9.8 m/s

2

×

-2.0 m=-78 J

. To verify that this is correct, note that since the cat changes the potential energy to kinetic energy by jumping, the potential energy decreases. Hence, the potential energy should be negative.

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