Question

Which equation would best help solve the following problem? Rennie kicks a field goal with an initial vertical velocity of 31 m/s. How long will it take the football to hit the ground?

–4.9t2 + 31t = 0


–4.9t2 – 31t = 0


16t2 + 31t = 0

–16t2+ 31t = 0

Answer 1

a=g

v=⌠a

v=gt+vi

h=⌠v

h=gt^2/2+vit+hi

So height as a function of time is:

h(t)=gt^2/2+vit+hi

g=-9.8m/s^2, vi=31m/s, hi=0 so

h(t)=-4.9t^2+31t

And it will hit the ground when h(t)=0 so

-4.9t^2+31t=0