# physics

a rock is thrown vertically down from a bridge with an initial velocity of 30m/s and strikes the water in 2.0sec. find the velocity with which the rock strikes and the height of the bridge.

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1. vi=-30m/s
a=-g=-9.8 m/s²
vf=vi+at
=-49.6 m/s
Height
=average velocity*time
=(-30-49.6)/2 * 2 sec
=-79.6 m
The negative sign means that the rock is lower than the initial position.

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