498_Physics ProblemsTechnical Physics

498_Physics ProblemsTechnical Physics - 500 P17.3 Sound...

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500 Sound Waves P17.3 Sound takes this time to reach the man: 20 0 1 75 343 532 10 2 .. . m m ms s af so the warning should be shouted no later than 0 300 5 32 10 0 353 2 . s s s = before the pot strikes. Since the whole time of fall is given by yg t = 1 2 2 : 18 25 1 2 980 2 m s 2 = ej t t = 193 . s the warning needs to come 1 93 0 353 1 58 . s s −= into the fall, when the pot has fallen 1 2 9 80 1 58 12 2 2 . s m 2 = to be above the ground by 20 0 12 2 7 82 ... m m P17.4 (a) At 9 000 m, T = F H G I K J −° = 9000 150 100 600 CC so T =− ° 30 0 .C . Using the chain rule: dv dt dv dT dT dx dx dt v dv dT dT dx v v == = F H G I K J = 0607 1 150 247 . , so dt dv v = 247 s dt dv v t v v t v v f i i f 0 247 247 247 331 5 0 607 30 0 331 5 0 607 30 0 zz = = F H G I K J = + +− L N M O Q P s s a f a f a f a f a f ln ln . . t = 27 2 . s for sound to reach ground. (b) t h v + = 331 5 0 607 30 0 25 7 . . a f s It takes longer when the air cools off than if it were at a uniform temperature.
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