29_Physics ProblemsTechnical Physics

29_Physics ProblemsTechnical Physics - 30 *P2.23 Motion in...

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30 Motion in One Dimension *P2.23 (a) Choose the initial point where the pilot reduces the throttle and the final point where the boat passes the buoy: x i = 0, x f = 100 m, v xi = 30 m s, v xf = ?, a x = 35 . ms 2 , t = ? xx v t a t fix i x =+ + 1 2 2 : 100 0 30 1 2 2 m m s m s 2 =+ + a f ch tt . 175 30 100 0 2 . m s m s m 2 af += . We use the quadratic formula: t bb a c a = ± 2 4 2 t = ± () = ± = 30 900 4 1 75 100 2175 30 141 12 6 ms m s m ±ms s 22 2 2 2 . . . . . or 453 s . The smaller value is the physical answer. If the boat kept moving with the same acceleration, it would stop and move backward, then gain speed, and pass the buoy again at 12.6 s. (b) vva t xf xi x =+= = 30 3 5 4 53 s 2 ... ej P2.24 (a) Total displacement = area under the vt , curve from
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