a boy stands on the edge of a cliff of height 60m.he throwws a stone upward so that its distance ,h m,above the cliff top is given by h=20t-5t^(b)calculate the time which elapses before the stone hits the beach(c)calculate the speed with which the st
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a boy stands on the edge of a cliff of height 60m.he throwws a stone upward so that its distance ,h m,above the cliff top is given by h=20t-5t^
(b)calculate the time which elapses before the stone hits the beach
(c)calculate the speed with which the stone hits the beach
我们不防设在从抛出石头到石头到最高点的时间为t1,下落时从悬崖边缘到底部的运行时间为t2.
则有 t =2* t1+t2; (1)
从最高点到悬崖边缘的 高度为h;
h = 20t-5t^ = g * t1^/2; (2)
从最高点到底部的高度为 h + 60;
h+60 = g * (t1+t2)^/2; (3)
由于 运算方便,所以我把g取了 10 ;
整理后就是一个 2元2次方程,不难解出 t t1 t2;
t是你要的时间 最后的速度 v= g*(t1 + t2);
具体结果由于时间原因我没有算,你自己算一下吧.
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