A ball is thrown upward from the ground with an initial speed of 23.2 m/s; at the same instant, another ball is dropped from a building 20 m high. After how long will the balls be at the same height?

Answer 1

let up be +

ball first:
h=23.2*t-4.9t^2
ball second
h=20-4.9t^2 set the two equations equal, solve for t. Notice is is a pretty simple solution.