Question

A person standing on the roof of a building drops a 0.125 Kg ball on the ground. A

child on eight floor saw the ball passing with a speed of 33.1 m/s. The first floor of the building

is 12.0 m high and each successive floor is 8.00 m high. Determine the total numbers of floors

in the building. How fast was the ball falling just before it hit the ground? What was its kinetic

energy just before it hit the ground?

Answer 1

V = a t velocity after time t

t = 33.1 / 9.80 = 3.38 sec (time ball had been falling)

S = 1/2 a t^2 = 55.9 m

So the ball had been falling for 7 * 8 = 56 m

The child was 7 floors from the top

Since he was on the eight floor the floors below him were

7 * 8 + 12 = 68 m total floors below child

68 + 56 = 124 m total height of building

Total floors in building = 7 + 7 + 1 = 15 floors

PE at top = KE at bottom

KE = m g h = .125 * 9.80 * 124 = 152 Joules