h=-t^2+3t+28

Question

A model rocket is shot straight up from the roof of a school. The height at any time t is approximated by the model h=-t^2+3t+28,where h is the height in meters and t is the time in seconds when does the rocket hit the ground?

Answer 1

when the rocket hits the ground h=0

0=-t^2+3t+28

t^2-3t-28=0

t^2-7t+4t-28=0

t(t-7)+4(t-7)=0

(t-7)(t+4)=0

t=7seconds ( t=-4 is to be omitted........ _ve value)

Answer 2

h(t) = t2 – 3t + 1. Evaluate h(6)