h=128t-16t^2, where h is the height, in feet, above the ground after t seconds. After how many seconds will the rocket be at a height of 240 feet?

Question

h=128t-16t^2

h=height in feet

t=time in seconds

when h=240, t=?

Answer 1

So the quadratic equation would be: 

-16 t² + 128t - 240 = 0

 

Simplify by dividing by 16, we get - t² + 8 t - 15 = 0

=> ( -t + 3)(t - 5). Since t can't be negative, t = 5 seconds