Question 125190
 {{{h= -16t^2+112t}}} is your equation for height.  Since you are given the height of 180 ft., just replace h with 180 and solve it like any other quadratic equation.


{{{-16t^2+112t=180}}}


{{{-16t^2+112t-180=0}}}


If you divide through by -4, the coefficients become a little more manageable:


{{{4t^2-28t+45=0}}}


You can use the quadratic formula if you don't want to scratch your head over the factorization of this one, but the factors come out to:


{{{(2x-9)(2x-5)=0}}}


So, {{{x=9/2}}} or {{{x=5/2}}}


Therefore, the arrow will be 180ft above the ground 2.5 seconds after it is released on the way up, and again at 4.5 seconds on the way down.