A mass $m_1$ of $100$ $kg$ traveling with a uniform velocity of $5$ $m/s$ along a line collides with a stationary mass $m_2$ of $1000$ $kg$. After the collision, both the masses travel together with the same velocity. The coefficient of restitution is
- $0.6$
- $0.1$
- $0.01$
- $0$