Two equal masses X and Y are travelling towards one another on a frictionless air track, as shown. The masses undergo an elastic collision. Which row shows possible velocities of the two masses after the collision?
- Avelocity of X: zero; velocity of Y: $20\ \text{cm s}^{-1}$ to the right
- Bvelocity of X: $10\ \text{cm s}^{-1}$ to the right; velocity of Y: $10\ \text{cm s}^{-1}$ to the right
- Cvelocity of X: $20\ \text{cm s}^{-1}$ to the left; velocity of Y: zero
- Dvelocity of X: $30\ \text{cm s}^{-1}$ to the left; velocity of Y: $50\ \text{cm s}^{-1}$ to the right