A body of mass 2 kg moving at 3 m s-1 collides and sticks to a stationary body of mass 4 kg. The common velocity after impact is

  • A. 0.5 m s-1
  • B. 1 m s-1
  • C. 1.5 m s-1
  • D. 2 m s-1

Explanation

Momentum is conserved, so the initial momentum of 2 times 3, which is 6 kg m s-1, is shared by the combined mass of 6 kg, giving a velocity of 1 m s-1. This is a perfectly inelastic collision, so kinetic energy is not conserved even though momentum is. Only the moving body contributes momentum, since the other starts at rest.

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