A body of mass 2 kg moving at 3 m per second collides and sticks to a stationary body of mass 4 kg. Their common velocity is

  • A. 1 m per second
  • B. 1.5 m per second
  • C. 0.5 m per second
  • D. 3 m per second

Explanation

Total momentum before is 2 multiplied by 3, that is 6 kg m per second, and the combined mass afterwards is 6 kg, so the common velocity is 1 m per second. The kinetic energy falls from 9 J to 3 J, the difference going into heat and deformation. Momentum is conserved even though energy is not.

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