A woman on a bridge 80.5 m high sees a raft floating at a constant speed on the

Question

A woman on a bridge 80.5 m high sees a raft floating at a constant speed on the river below. She drops a stone from rest in an attempt to hit the raft. The stone is released when the raft has 8.91 m more to travel before passing under the bridge. The stone hits the water 5.59 m in front of the raft. Find the speed of the raft.

Explanation / Answer

initial velocity of stone, u = 0m/s height from where stone is dropped, h = 80.5m acceleration = 9.8m/s^2 BY newton;s laws of motion, v^2=u^2 + 2as => v^2 = 2 x 9.8 x 80.5 => v^2 = 1577.8 => v = 39.72m/s By newton's laws of motion, v = u +at => t = (v-u)/a => t = 39.72/9.8 => t = 4.05s the time taken by stone is equal to the time taken by the raft to move from being 8.91m away from bridge to 5.59m ================================motion of raft => S = 3.32m time to travel this distance = 4.05 therefore speed of raft = s/t = 3.32/4.05 = 0.8197m/s...

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