h=-t^2+3t+28 If h is height in metres and t is time in seconds, when does the rocket hit the ground?

Answer 1

The rocket hits the ground at the time t > 0 when h(t) = 0. Solving the equation -t² + 3t + 28 = 0, one obtains t = -4 and t = 7. The positive t-solution, t = 7 s, is the time required.