7.34. Set Up: Solve for k in part (a). Use for part (b), and for part (c). Solve: (a) The force constant of the spring is: (b) (i) and (ii) The elastic potential energy is the same whether the spring is stretched or compressed: (c) The work done on the spring is equal to the spring’s gain in potential energy: 7.35. Set Up: Use In part (a), equals mg , the weight of the object suspended from it. In part (b), also apply to calculate the stored energy. Solve: (a) (b) Reflect: The 250 g object has a weight of 2.45 N. The 138 N force is much larger than this and stretches the tendon a much greater distance. 7.36. Set Up: Use for the potential energy. for and for are related by Solve: (a) (b) depends only on the magnitude of x , not on its sign; therefore, the elastic potential energy is (c) (d) 7.37. Set Up: Use for part (a) to assess the spring constant and for (b) to determine the spring length required to achieve 850 J of stored energy. Solve: (a)
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