Question: An inflatable raft (unoccupied) floats down a river at an approximately constant speed of 3.9 m/s. A child on a bridge, 66 m above the river, sees the raft in the river below and attempts to drop a small stone onto the raft. The child releases the stone from rest.
Part A: In order for the stone to hit the raft, what must be the horizontal distance between the raft and the bridge when the child releases the stone?
I want to know how to work this out step by step, not just the answer please.