physics
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.
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