Posted by Cecille on .
I fire a tennis ball from an air cannon, straight up from ground level, at initial speed v0. At
the instant it reaches the top of its trajectory, I fire a second tennis ball at the same initial
speed. Air resistance is negligible. At what fraction of the maximum height reached by the
first ball do the two collide?

Physics 
bobpursley,
start ball one at max height:
hf=maxheight1/2 g t^2
ball two:
hf=vo*t4.9t^2
but t is the same, and hf is the same:
set the two equations equal, and solve for t.
then having t, find hf.