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A .20 kg stone is held 1.3 m above the top edge of a water well and then dropped

ID: 2144187 • Letter: A

Question

A .20 kg stone is held 1.3 m above the top edge of a water well and then dropped into it. The well has a depth of 5.0 m. If the gravitational potential energy of the stone-Earth system is defined to be zero when the stone is at the top edge of the well, what is the gravitational potential energy of the stone-Earth system (a) just before the stone is dropped, and (b) just as it reaches the bottom of the well? (c) What is the change in the gravitational potential energy of the system from release to reaching the bottom of the well?

Explanation / Answer

a) E1 = PE = m g h


E1 = 0.20 * 9.81 * 1.3


= 2.55 J


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b) E2 = 0.20 * 9.81 * (-5.0)

= - 9.81 J


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c) Change = E2 - E1

= -9.81 - 2.55

= -12.36 J