Question #262467

A girl is standing at the edge of a cliff 100. m above the ground. She reaches out over the edge of the cliff and throws a rock straight upward


with a speed 8.00 m/s.


a) How long does it take the rock to hit the ground?


b) What is the speed of the rock the instant before it hits the ground?



I think the answers are:


a) 6.4s


b) 45.0m

1
Expert's answer
2021-11-07T19:24:50-0500

h=v22g=3.3 m,h'=\frac{v^2}{2g}=3.3~m,

H=h+h=103.3 m,H=h+h'=103.3~m,

a)

t=t1+t2=2hg+2Hg=5.4 s,t=t_1+t_2=\sqrt{\frac{2h'}g}+\sqrt{\frac{2H}g}=5.4~s,

b)

u=2gH=45 ms.u=\sqrt{2gH}=45~\frac ms.


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