Solutions to HW# 8.doc

# Solutions to HW# 8.doc - Solutions to Exercises Problems 1E...

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Solutions to Exercises & Problems 1E As the particle moves from point A to point B, the work W done by F is equal to the loss of the corresponding potential energy of the system: W = ? _U AB = U A ? U B . Thus U B = U A ? W = 40 J ? 25 J = 15 J. 2E The elastic potential energy stored in the spring is given by U = 1 2 kx 2 , where k is the spring constant and x is the displacement of the end of the spring from its position when the spring is in equilibrium. Thus k = 2U x 2 = (2)(25 J) (0:075 m) 2 = 8:9 _ 10 3 N/m: 3E (a) The vertical drop of the book of mass m is h = (10:0m ? 1:50 m) = 8:50 m. The work done by the weight of the book is W = mgh = (2:00 kg)(9:80 m/s 2 )(8:50 m) = 167 J. (b) The change in the gravitational energy of the textbook-Earth system is related to W by _U = ? W. Thus _U = ? 167 J. (c) and (d) Denote the potential energy as U
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