A toy rocket is launched into the air at an initial velocity of 32 ft/sec, as shown on the graph below. The function s(t)=-16t^2+32t+128 gives the height of the rocket (in feet) at time t (seconds). When does the rocket hit the ground? Show your work.

Answer 1

the ground is zero feet

0 = -16t^2 + 32t + 128

dividing by -16 ... 0 = t^2 - 2t - 8

factoring ... 0 = (t - 4) (t + 2)

0 = t - 4 ... t = 4