h = 1/2 g t^2
h-20=1/2 g (t - 1)^2 ... h = 1/2 g t^2 - g t + 1/2 g + 20
the h's equal zero when the ball reaches the ground
... set the equations equal and solve for t
... plug the value of t into the 1st equation to find h
a ball is dropped from height h after one second another ball dropped freely from point 20 m below where first ball dropped both of them reach the grount at the same time calculate the value of h
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