A ball is dropped from a cliff and 2 seconds later, a second ball is thrown vertically downward. What must be the initial velocity of the second ball if it overtakes the first ball as it passes 400m ?

Answer 1

If you mean that the balls pass as they have both fallen 400m, then you have

4.9t^2 = 400
v(t-2)+4.9(t-2)^2 = 400

v(20/√4.9-2)+4.9(20/√4.9-2)^2 = 400
v = 22.39 m/s