A boy throws a stone vertically down from a cliff top at aninitial velocity of 1

Question

A boy throws a stone vertically down from a cliff top at aninitial velocity of 15.0m/s down. the cliff top is 85.0 abovethe ground. (a) what is the velicity of the stone as it is about tostrike the ground? (b) How long does it take the stone to reach the ground? A boy throws a stone vertically down from a cliff top at aninitial velocity of 15.0m/s down. the cliff top is 85.0 abovethe ground. (a) what is the velicity of the stone as it is about tostrike the ground? (b) How long does it take the stone to reach the ground?

Explanation / Answer

a)Take origin at top of cliff. We have v0x=15distance in negative y direction -85 Use equation of motion for constant acceleration that does notinvole t. The fianl velocity is: vf2=v0y2+2ay(y-y0) ay=-9.8,   y-y0=-85 vf=-43.5m/s (speed is 43.5, velocity is-43.5) b) To find t vf=v0y+ayt Now v0y=-15 so Sustituting we have t=2.9s

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