Word problem help? 5

Question

An object is thrown upward from the top of a 160 foot building with an initial velocity of 144 feet per second. The height h of the object after t seconds is given by the quadratic equation h=-16t^2+144t+160. When will the object hit the ground?

 

 

The object will hit the ground at when the time is ___ seconds

Answer 1

Set h = 0 since it will hit the ground at that point.  Solve the equation

0 = -16t^2 + 144 t + 160

Factor out 16

-t^2 + 9t + 10 = 0

Solve for t

t = -1 or 10

Since you can not go backward in time,

t = 10 sec

Plug in 10 sec to verify result

-16*10^2 + 144*10 + 160 =  0

Problem verified