posted by Keith .
a girl throws a ball vertically upwards at 5m/s from the roof of a building 20m high
how long will it take the ball to reach the ground? and what will its speed be when it strikes the ground
when at the top, vertical velocity is zero
vf=0=vi+gt solve for t, time to top.
How long it will take to get to the ground?
Hf=Hi+vi*t-1/2 g t^2 hi=20, hf=0, solve for t to get time in the air.