Question

A boy lining a railway bridge 49ft. high, sees a train uproaching with uniform speed and attempt to drop a stone down to railway. He releases the stone when engine is 80ft. away from the point below his position and sees the stone hits in the ground just 3 ft. in front of the engine. What is the speed of train in miles per hour?

Answer 1

Kinematics equation with zero initial velocity:
h=(1/2)gt^2 =>
time, t = √(2h/g) seconds
h=49', g=32.2 ft/s²
speed = distance/time
= (80-3)/t ft/s
=44.14 fps