Yes. the mass m is needed.

Initial velocity is zero, so W=\tfrac{1}{2}mv^2=kq_1 q_2 (\frac{1}{r_0}-\frac{1}{r})

so v(r)= \sqrt{\frac{2kq_1 q_2}{m}(\frac{1}{r_0}-\frac{1}{r})}