a ball is thrown from an initial height of 7ft with an initital upward velocity of 31 ft/s.

Question

a ball is thrown from an initial height of 7ft with an inital upward velocity of 31ft/s. find all values of t for which yhe balls height is 21 ft

Answer 1

h(t) = -16t² + 31t + 7

 

Set h(t) = 21

 

21 = -16t² + 31t + 7

 

-16t² + 31t - 14 = 0

 

Solve this quadratic equation for t, which you should know how to do.  You will get two values of t.  The lower value is the time to reach 12 on the way up, and the higher value is the time to reach 12 again, but on the way down.