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Further Mechanics

Elastic and inelastic collisions

  • 2 things to know
  • Papers 1 and 3

Overview

Recall questions on the definitions, the calculation that distinguishes them, where the missing kinetic energy goes, and whether a collision can lose all of it.

What you need to know

Answer each one before you reveal it.

Your recallNot started
Numbers

What is an example of a nearly perfectly elastic collision, and can a collision lose all of its kinetic energy?

Process

What calculation decides whether a collision is elastic or inelastic, and what happens in a perfectly inelastic one?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What is an elastic collision?

    Model answer

    An elastic collision is one in which total kinetic energy is conserved as well as total momentum.

  2. 2

    What is an inelastic collision?

    Model answer

    An inelastic collision is one in which momentum is conserved but total kinetic energy is not, some being transferred to other forms.

  3. 3

    Is momentum conserved in an inelastic collision?

    Model answer

    Yes, momentum is conserved in every collision in which no resultant external force acts, whether kinetic energy is conserved or not.

  4. 4

    What calculation do you carry out to decide whether a collision is elastic or inelastic?

    Model answer

    Work out the total kinetic energy of all the bodies before the collision and again afterwards; if the two totals are equal the collision is elastic, and if the total falls it is inelastic.

  5. 5

    In an inelastic collision, where does the missing kinetic energy go?

    Model answer

    It is mainly transferred to internal (thermal) energy of the colliding bodies, with smaller amounts going to sound and to permanent deformation.

  6. 6

    In a perfectly inelastic collision, what happens to the momentum and to the kinetic energy?

    Model answer

    Momentum is conserved, as in any collision, but the kinetic energy falls by the largest amount that conservation of momentum allows, because the bodies move off together with a common velocity.

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