A ball is dropped from a height of 3000 feet. Its velocity after t seconds is $v(t)=-78t$.
a) How fast is the ball dropping after 5 seconds?
b) Determine the position function $s=s(t)$.
For a), I multiplied $64$ by $5$ and got $320$. But, I'm currently stuck on b); I got $s(t)=-32t^2+c$, but I can't figure out how to calculate the $c$ value, because there is no $s(0)=0$. Thank you!