253_Physics ProblemsTechnical Physics

253_Physics ProblemsTechnical Physics - Chapter 9(a The...

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Chapter 9 255 P9.5 (a) The momentum is pm v = , so v p m = and the kinetic energy is Km v m p m p m == F H G I K J = 1 2 1 22 2 2 2 . (b) v = 1 2 2 implies v K m = 2 , so vm K m mK = 2 2. Section 9.2 Impulse and Momentum *P9.6 From the impulse-momentum theorem, Ft pm v m v fi ∆∆ a f , the average force required to hold onto the child is F mv v t = = F H G I K J =− × di af bg b g 12 0 60 0050 0 1 2237 644 10 3 kg mi h s ms mi h N .. Therefore, the magnitude of the needed retarding force is 3 . × N , or 1 400 lb. A person cannot exert a force of this magnitude and a safety device should be used. P9.7 (a) IF d t z area under curve I = 1 2 150 10 18000 135 3 s N
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