Two blocks, P and Q, move towards one another on a horizontal frictionless surface. They undergo an elastic collision. The diagram indicates the velocities of the two blocks immediately after the collision. Which row shows a possible pair of velocities for the two blocks just before the collision?
- Avelocity of P: $10\text{ cm s}^{-1}$ to the right; velocity of Q: $60\text{ cm s}^{-1}$ to the left
- Bvelocity of P: $50\text{ cm s}^{-1}$ to the right; velocity of Q: zero
- Cvelocity of P: $20\text{ cm s}^{-1}$ to the left; velocity of Q: $70\text{ cm s}^{-1}$ to the right
- Dvelocity of P: $60\text{ cm s}^{-1}$ to the right; velocity of Q: $30\text{ cm s}^{-1}$ to the left