標題:
請指教-應用那鑄幾條公式
發問:
以一名體重約150磅（約70公斤）的成年人計算，從62米高處墮海，約需3.6秒，入水前時速126公里，若身體「打橫」撞擊入水，其撞擊力高達686磅； 已有高度, 重量, 但秒, 時速, 撞擊力 是如何推算出來 應用那幾條公式 請指教
Given: mass of person = 70 kg, falling height = 62 m Use equation of motion: v^2 = u^2 + 2a.s with u = 0 m/s, a = g(=9.81 m/s^2), s = 62 m v =? hence, v^2 = 2 x 9.81 x 62 (m/s)^2 i.e. v = 34.88 m/s = 126 km/h Speed before striking the water surface = 126 km/h Use equation of motion: s = ut + (1/2)at^2 with s = 62 m, u = 0 m/s, a = g(=9.81 m/s^2), t =? hence, 62 = (1/2).(9.81)t^2 t = 3.56 s The time of fall = 3.56 s You need to make an assumption on the impact time on the water surface, just assume it to be 1 s (in order of magnitude). Use equation: impulse (衝量) = change of momentum (動量改變) (F - 70g) x 1 = 70 x 34.88 where F is the impact force (衝擊力) solve for F gives F = 3128 N = 3128/9.81 kgf = 318.9 kgf = 318.9 x 2.2 lbf = 702 lbf
其他解答:63D0B758E2D502CC
請指教-應用那鑄幾條公式
發問:
以一名體重約150磅（約70公斤）的成年人計算，從62米高處墮海，約需3.6秒，入水前時速126公里，若身體「打橫」撞擊入水，其撞擊力高達686磅； 已有高度, 重量, 但秒, 時速, 撞擊力 是如何推算出來 應用那幾條公式 請指教
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最佳解答:Given: mass of person = 70 kg, falling height = 62 m Use equation of motion: v^2 = u^2 + 2a.s with u = 0 m/s, a = g(=9.81 m/s^2), s = 62 m v =? hence, v^2 = 2 x 9.81 x 62 (m/s)^2 i.e. v = 34.88 m/s = 126 km/h Speed before striking the water surface = 126 km/h Use equation of motion: s = ut + (1/2)at^2 with s = 62 m, u = 0 m/s, a = g(=9.81 m/s^2), t =? hence, 62 = (1/2).(9.81)t^2 t = 3.56 s The time of fall = 3.56 s You need to make an assumption on the impact time on the water surface, just assume it to be 1 s (in order of magnitude). Use equation: impulse (衝量) = change of momentum (動量改變) (F - 70g) x 1 = 70 x 34.88 where F is the impact force (衝擊力) solve for F gives F = 3128 N = 3128/9.81 kgf = 318.9 kgf = 318.9 x 2.2 lbf = 702 lbf
其他解答:63D0B758E2D502CC
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