Question

A ball B1 is dropped from the top of a building, one second later another ball, B2 is thrown down with an initial speed of 20.0m/s. The two balls hit the ground at the same time.

1)What is the time it took B1 to teach the ground?

2) What is the height of the building?

3)what are the speeds of the two balls at the instant they hit the ground?

Answer 1

t is time for ball 2
t+1 is time for ball 1

h = (1/2)g (t+1)^2
h = 20 t + (1/2)gt^2
so
g(t+1)^2 = 40 t + gt^2
g(t^2 + 2 t + 1) = 40 t + g t^2
2 gt + g = 40 t
t = g (2t+1)/40
t+1 = answer to 1) etc

Answer 2

2 g t + g = 40 t
(40 -2g)t = g
t = g/(40-2g)