posted by lee .
If a ball is thrown upwards at 20 ft/sec, the height h after t seconds is given by h = -16t^2 + 20t. How many seconds does it take for the ball to reach its maximum height, and what is this height?
at max height, Velocity is zero.
v=dh/dt=-32t+20=0 t= 20/32 seconds
calculate h at this time.