word problem

Question

The height in feet, h, reached by a projectile after t seconds is given by the function:

h(t) = -16t^2 + 110t + 5

When will the projectile reach a height of 122 feet on its way down?

Answer 1

Just set h(t) = 122 and solve for t.

 

122 = -16t² + 110t + 5

 

-16t² + 110t - 117 = 0

 

Solve this quadratic equation for t.  You should get 2 values.  The lower value is the time it takes to reach 122 feet on the way, and the lower value is the time it takes to reach 122 feet on the way down.