A space probe is traveling in the $+x$-direction with speed $v_0$ very far from any other objects. A small explosive device inside the space probe is detonated and the space probe breaks into two pieces with masses $m_1$ and $m_2$. The piece with mass $m_1$ moves in the $+x$-direction with speed $2v_0$. Which of the following is an expression for the velocity of the piece with mass $m_2$?
A $\frac{m_1}{m_2}v_0$
B $\frac{2m_1}{m_2}v_0$
C $\frac{(m_2-m_1)}{m_2}v_0$
D $\frac{(m_2+m_1)}{m_2}v_0$