You drop a 2.30 kg textbook to a friend who stands on the ground at distance D =

Question

You drop a 2.30 kg textbook to a friend who stands on the ground at distance D = 10.0 m below. Your friend's outstretched hands are at distance d = 1.50 m above the ground. How much work Wg is done on the textbook by its weight as it drops to your friend's hands if U is 100 J at the ground level. What is the change Delta U in the gravitational potential energy of the textbook-Earth system during the drop if U is 100 J at the ground level. Find U at the release point when U is 100 J at the ground level. Find U at the hands when U is 100 J at the ground level.

Explanation / Answer

The work done is W = m g ( D - h)       = 2.3(9.8)(10-1.5)       = 191.6J ---------------------------------------------------------------------------------------------------------------- b) change in gravitational potential energy    U = - W = - 191.6 J ----------------------------------------------------------------------------------------------------------------- c) energy at relaease point is    U = m g D + 100       = 2.3(9.8)(10) + 100      = 325.4 J ---------------------------------------------------------------------------------------------------------------- d) energy at the hand     U = m g d + 100        = (2.3)(9.8)(1.5) +100        = 133.8 J

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