posted by Mark .
Assume acceleration due to gravity=10 m/s. A ball is thrown vertically upward from top of a building with speed of 20 m/s. On the way back ball misses the building and lands on the ground. Total time the ball is in air is 6 seconds. Determine the height of the building with speed of 30 m/s.
The ball's rise time derives from 0 = 20 - 10t or t = 2sec.
During this 2 sec. period, it climbs to
h = 20(2) - 5(2)^2 = 20m.
The time for the ball to reach the ground is 6 - 2 = 4 sec.
The distance covered in 4 sec. derives from
h = 0 + 5(4)2 = 80m. making the building 80 - 20 = 60m high.