Edexcel A-Level Physics 9PH0
Working as a Physicist
Mechanics
Electric Circuits
Materials
Waves and Particle Nature of Light
Further Mechanics
Electric and Magnetic Fields
Nuclear and Particle Physics
Thermodynamics
Space
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Gravitational Fields
Oscillations
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.
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
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
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
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
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
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
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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