일반물리학 1 — Potential Energy and Conservation of Energy: Problem 3

3 You drop a 2.00 kg book 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 (Fig. 8-19). (a) How much work $W_g$ does the gravitational force do on the book as it drops to her hands? (b) What is the change $\Delta U$ in the gravitational potential energy of the book–Earth system during the drop? If the gravitational potential energy $U$ of that system is taken to be zero at ground level, what is $U$ (c) when the book is released, and (d) when it reaches her hands? Now take $U$ to be 100 J at ground level and again find (e) $W_g$, (f) $\Delta U$, (g) $U$ at the release point, and (h) $U$ at her hands.