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prob_119

# prob_119 - 119 CONCEPT QUESTIONS a The block is in...

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119. CONCEPT QUESTIONS a. The block is in equilibrium in each case. Since the block moves at a constant velocity in each case, it is not accelerating. A zero acceleration is the hallmark of equilibrium. b. The direction of the kinetic frictional force is not the same in each case. The frictional force always opposes the relative motion between the surface of the block and the wall. Therefore, when the block slides upward, the frictional force points downward. When the block slides downward, the frictional force points upward. These directions are shown in the free-body diagrams (not to scale) for the two cases. In these diagrams W is the weight of the block and f k is the kinetic frictional force. c. In each case the magnitude of the frictional force is the same. It is given by Equation 4.8 as f k = μ k F N , where μ k is the coefficient of kinetic friction and F N is the magnitude of the normal force. The coefficient of kinetic friction does not depend on the direction of the motion.

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prob_119 - 119 CONCEPT QUESTIONS a The block is in...

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