A girl throws a ball vertically upwards at 10m/s from the roof of a building 20m high. How long will it take the ball to reach the ground? What will its speed be when it strikes the ground?

Answer 1

since the height

h = 10t - 4.9t^2, you want t when h=0.

similarly, v = 10-9.8t

Answer 2

1.24