a toy rocket is launched from a 5.6m high platform

Question

a toy rocket is launched from a 5.6m high platform in such a way that its height, h (in meters), after t seconds is given by the equation h=-4.9t^2+38.5t+5.6. how long will it take for the rocket to hit the ground?

Answer 1

h is how far above the ground you are. notice in the beginning when t=0, h=5.6 cuz that's how far above the ground the rocket was at take off. when it hits the ground h=0.

so we let h=0 and solve for t

0 = -4.9t^2+38.5t+5.6

using the quadratic formular i get t = -1/7 and 8 seconds, so the answer is really 8!!! (we can't have negative time cuz we don't have a time machine yet)