If a body having mass m1 (2 kg) moving with 5 m/s approaches another mass m2 (3 kg) with speed of 1 m/s in same direction, relative speed of approach is 4 m/s. Relative speed of separation after collision will be:
- A. 4 m/s
- B. 2 m/s
- C. 6 m/s
- D. Depends on masses
Explanation
For a perfectly elastic collision the relative speed of separation equals the relative speed of approach, whatever the masses, which follows from conserving both momentum and kinetic energy. So the 4 m per second closing speed becomes a 4 m per second separating speed. In an inelastic collision the separation speed would be smaller, and in a perfectly inelastic one it would be zero.
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