Motion questions

Question

a ball is thrown straight up from the edge of a building and takes 1.3 seconds to reach its highest point. it continues on its flight and falls to the ground, taking an additional 3.3 seconds ( for a total time in the air of 4.6 seconds). how tall is the building?

Answer 1

Given acceleration of gravity = -9.8 m/sec, the ball's initial velocity was 12.74 m/sec (1.3 * 9.8) upward and its final velocity was 32.34 m/sec (3.3 * 9.8) downward.

 

The ball traveled 8.28 m upward.  (Multiply time of upward flight - 1.3 sec -  by mean upward velocity, which is the sum of initial upward velocity - 12.74 m/sec - and final upward velocity - 0 m/sec - divided by 2.)

 

Then the ball traveled 53.36 m downward.  (Multiply time of downward flight - 3.3 sec - by mean downward velocity, which is the sum of initial downward velocity - 0 m/sec - and final downward velocity - 32.34 m/sec - divided by 2.)

 

Subtract upward distance from downward distance.  53.36 m - 8.28 m = 45.08 m.  This is the height of the building.