The most interesting thing about this problem is that in order to use all of the given information, you need to ignore the laws of Physics, and never mind what the stone would really do if dropped from a real bridge in the real world.
Average velocity = (displacement) / (time for the displacement)
Displacement =
Straight path from the start point to the finish point = 45 meters down .
Time = 4.6 seconds
Average velocity = 45/4.6 = 9.783 meters/second down
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In the real world, a dropped stone would only take 3.03 seconds
to fall 45 meters.
Alternatively, a stone that fell for 4.6 seconds from rest would fall
103.7 meters, with an average velocity of 22.5 meters/second down.
But we accepted the given information, and did the best we could do
with it.
