You drop a 1.90 kg book to a friend who stands on the ground at distance D = 11.
ID: 1552017 • Letter: Y
Question
You drop a 1.90 kg book to a friend who stands on the ground at distance D = 11.0 m below. If your friend's outstretched hands are at distance d = 1.50 m above the ground (see the figure), (a) how much work Wg does the gravitational force do on the book as it drops to her hands? (b) What is the change 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) Wg, (f ) U, (g) U at the release point, and (h) U at her hands.
You drop a 1.90 kg book to a friend who stands on the ground at distance D = 11.0 m below. It your friend's outstretched hands are at distance d = 1.50 m above the ground (see the figure) (a) how much work W_g does the gravitational force do on the book as it drops to her hands? (b) What is Delta U in the gravitational energy of the book Earth system during the drop? If the gravitational energy U of that system to be zero at ground level, what level 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.Explanation / Answer
(a) Work = FS
Work = mg(h) = 1.90kg(9.8)(11.00m -1.50m)
Work = 176.89J
(b)Relative to ground level, PE = mg(10) =(1.90)(9.8)(11) = 204.82J
As it drops PE became PE = mg(1.5) = 27.93J
Change in PE = 204.82 - 27.93 = 176.89J (equal to work done in dropping)
(c) 204.82J
(d) 27.93J
(e)Work Wg will not change because it is the difference in PE between two points, still Wg = 176.89J
(f) DU between what two points? (computer says not specified)
(h) PE at her hands = 27.93 + 100J = 127.93J
(g)U = 204.82J + 100J = 304.82J
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