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ｍｅｃｈａｎｉｃｓ

 

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發問:

A boy jumps up and his feet are 0.5m above the ground. (a)Find the hang-time of the boy. (b)Find the jumping speed of the boy. 點做？另外，題目內的ａ，ｕ，ｖ，ｓ，ｔ分別是什麼？

最佳解答:

In the question, take upward direction be positive. Acceleration, a = -10 ms-2 By v2 = u2 + 2as 0 = u2 + 2(-10)(0.5) Initial speed, u = 3.16 ms-1 Now, by v = u + at 0 = 3.16 - 10t t = 0.316 s So, the hang-time = 2t = 0.632 s b. The jumping speed = u = 3.16 ms-1 Inside the problem, acceleration, a = -10 ms-2 Initial speed, u = 3.16 ms-1 Final speed, v = -3.16 ms-1 displacement, s = 0 Hang-time, t = 0.632 s

其他解答:8758B59A7FA1EEA7
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