223_Physics ProblemsTechnical Physics

223_Physics ProblemsTechnical Physics - Chapter 8 P8.18 In...

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Chapter 8 225 P8.18 In the swing down to the breaking point, energy is conserved: mgr mv cos θ = 1 2 2 at the breaking point consider radial forces Fm a Tm g m v r rr = +− = max cos 2 Eliminate v r g 2 2 = cos g m g g T mg max max max cos cos cos cos cos . . . −= = = F H G I K J = F H G G I K J J −− θθ 2 3 3 44 5 980 40 8 11 N 32 .00 kg ms 2 bg ej *P8.19 (a) For a 5-m cord the spring constant is described by Fk x = , mg k = 15 . m a f . For a longer cord of length L the stretch distance is longer so the spring constant is smaller in inverse proportion: k L mg mg L KU U mgy mgy kx mg y y kx mg L x gs i f if f f f == ++ = + +=+ + = 5 333 00 0 1 2 1 2 1 2 2 22 m 1.5 m . . di initial final FIG. P8.19(a) here yy Lx f =+ 55 m 55 0 1 2 333550 55 0 5 04 10 183 1 67
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