Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
A spring with is squeezed by .
Gravitational potential energy near the Earth is , with measured from any level we choose; only changes in matter. A spring stores . The force is .
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Plan. .
Step 1. (a) .
Step 2. (b) Twice the squeeze gives times the energy: .
Answer: (a) . (b) .
Check. Directly: . Same.
Watch out. A squeezed spring stores energy just as a stretched one does: is positive either way.
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