245_Physics ProblemsTechnical Physics

245_Physics ProblemsTechnical Physics - 247 Chapter 8 P8.71...

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Chapter 8 247 P8.71 Applying Newton’s second law at the bottom (b) and top (t) of the circle gives Tm g mv R b b −= 2 and −− = g mv R t t 2 Adding these gives TT m g mv v R bt =+ + 2 22 ej Also, energy must be conserved and ∆∆ UK += 0 So, v mgR 2 02 0 +− = bg and v R mg 4 = Substituting into the above equation gives g 6 . mg v t T t mg T b v b FIG. P8.71 P8.72 (a) Energy is conserved in the swing of the pendulum, and the stationary peg does no work. So the ball’s speed does not change when the string hits or leaves the peg, and the ball
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