In a perfectly inelastic collision between two objects in a closed system, what happens to momentum and kinetic energy?

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Prepare for the Year 10 Force and Motion Test. Utilize flashcards and multiple-choice questions with clear hints and explanations to ensure success. Equip yourself for excellence on your exam!

Multiple Choice

In a perfectly inelastic collision between two objects in a closed system, what happens to momentum and kinetic energy?

Explanation:
Momentum is conserved in a closed system during collisions, but kinetic energy need not be conserved in inelastic collisions. In a perfectly inelastic collision, the two objects stick together and move with a common final velocity. Momentum must stay the same before and after, so m1 v1 + m2 v2 = (m1 + m2) v_final, giving v_final = (m1 v1 + m2 v2)/(m1 + m2). The kinetic energy after impact, KE_after = 1/2 (m1 + m2) v_final^2, is generally less than the initial kinetic energy, KE_before = 1/2 m1 v1^2 + 1/2 m2 v2^2, because some energy is transformed into internal energy like deformation, heat, and sound. Only in specific cases would KE be unchanged; in general it is not conserved here.

Momentum is conserved in a closed system during collisions, but kinetic energy need not be conserved in inelastic collisions.

In a perfectly inelastic collision, the two objects stick together and move with a common final velocity. Momentum must stay the same before and after, so m1 v1 + m2 v2 = (m1 + m2) v_final, giving v_final = (m1 v1 + m2 v2)/(m1 + m2). The kinetic energy after impact, KE_after = 1/2 (m1 + m2) v_final^2, is generally less than the initial kinetic energy, KE_before = 1/2 m1 v1^2 + 1/2 m2 v2^2, because some energy is transformed into internal energy like deformation, heat, and sound. Only in specific cases would KE be unchanged; in general it is not conserved here.

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