Grade 12 Physical Sciences · Mechanics

Decide if a collision is elastic

Compare total kinetic energy before and after a collision to decide if it is elastic (kinetic energy kept) or inelastic (kinetic energy lost).

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5)Elastic Inelastic Collisions | Intro part 1Kevinmathscience

5)Elastic Inelastic Collisions | Intro part 2Kevinmathscience

Grade 12 Elastic vs Inelastic collisions: MomentumMiss Martins Maths and Science

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Question 1.4 · May/June 2025 · Paper 1 · National (DBE) · 2 marks

Various options are provided as possible answers to the following questions. Each question has only ONE correct answer. Choose the answer and write only the letter (A–D) next to the question numbers (1.1 to 1.10) in the ANSWER BOOK, e.g. 1.11 E.

1.4 Two hard objects collide INELASTICALLY in an isolated system.

Which ONE of the following statements is CORRECT for this collision?(2)

A Both total momentum and total kinetic energy are conserved.
B Neither total momentum nor total kinetic energy is conserved.
C Total momentum is not conserved, but total kinetic energy is conserved.
D Total momentum is conserved, but total kinetic energy is not conserved.

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More past paper questions: decide if a collision is elastic

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3. Question 4.3 · November 2022 · Paper 1 · National (DBE) · 5 marks
Trolley X of mass $1, 2$ kg travels at $8$ m·s $^{- 1}$ east and collides with trolley Y of mass $0, 5$ kg which is initially at rest.

Ignore all frictional effects.

The velocity-time graph below shows the velocity of trolley X before, during and after the collision with trolley Y.
4.3 Is the collision ELASTIC or INELASTIC?

Explain the answer by means of suitable calculations.(5)
Show the memo (5 ticks)Memo
1. ✓
  ConclusionInelastic
  1 mark · Decide if a collision is elastic
2. ✓
  Formula $E_{k} = \frac{1}{2} m v^{2}$
  1 mark · Decide if a collision is elastic
3. ✓
  Substitution: kinetic energy before $\sum E_{ki} = \frac{1}{2} (1, 2) (8)^{2} + 0 = 38, 4$ J
  1 mark · Decide if a collision is elastic
4. ✓
  Substitution: kinetic energy after $\sum E_{k f} = \frac{1}{2} (1, 2) (4)^{2} + \frac{1}{2} (0, 5) (9, 6)^{2} = 32, 64$ J
  1 mark · Decide if a collision is elastic
5. ✓
  Comparison $\sum E_{ki} \neq = \sum E_{k f}$
  1 mark · Decide if a collision is elastic
4. Question 4.3 · May/June 2025 · Paper 1 · National (DBE) · 1 mark
Trolley A of mass $1, 5$ kg is at rest on a frictionless horizontal surface. A second trolley B, of mass $2$ kg, travelling horizontally at a constant speed v, collides with trolley A. The trolleys stick together and move at a constant velocity to the right, covering a distance of $0, 8$ m in $2$ s. See the diagram below.

Ignore ALL frictional and rotational effects.
4.3 Is the collision ELASTIC or INELASTIC?(1)
Show the memo (1 tick)Memo
1. ✓
  Type of collisionInelastic
  1 mark · Decide if a collision is elastic

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