Question

A missile fired straight up into the air has a height, in meters, given by h = -5t² + 45t, where t is the time, in seconds, the missile has been in the air. By setting up and solving an equation, find the times when the missile reaches a height of 90 meters. at seconds

Answer 1

Given: h = -5t^2 + 45 t , we want to know the time(s) that the missile reaches 90 meters .

Solution : set h = 90

90 = -5t^2 +45t

by setting the equation = 0 , we get :

-5t^2+45t -90 = 0 ........... ( divide both side by -5) you get

t^2-9 +18 = 0 ....................( solve for t )

(t - 3 )(t - 6)= 0

Therefore the missile reaches the height of 90meters when t = 3 seconds and t = 6 seconds