We solve this equation for v:
Now, to the possible values.
We cant calculate v when t=0 (divizion by 0). Also, t can not be negative, so v too. Then we find the minimum for v(t).
v^2;(t)=-25/t^2+1/4=0 so t=10 is a local minimum.
Minimal value for v is v(10)=(100+100)/40=5m/s maximum is any.
So the answer - v is equal or greater than 5 m/s.