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S5 Physics: Momentum and Collisions – Challenge Practice (10 Questions)
S5 Physics: Momentum and Collisions – Challenge Practice (10 Questions)
Elastic collisions and harder applications: 2 kg at 3 m/s on 4 kg gives minus 1 and 2 m/s, equal masses exchange speeds, 1 kg at 8 m/s on 3 kg gives minus 4 and 4, a 0.15 kg ball reversing 28 m/s in 0.02 s needs 210 N, and a bullet in a block gives 4 m/s.
Quick answer Elastic results: 2 kg at 3 m/s on 4 kg gives minus 1 and 2 m/s, equal 3 kg masses exchange to 0 and 6, 1 kg at 8 m/s on 3 kg gives minus 4 and 4, 4 kg on 2 kg gives eight thirds; a 0.15 kg ball needs 210 N; two 1 000 kg cars lose 25 000 J; a bullet in a block gives 4 m/s.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 questions |
| Suggested time | about 30 minutes |
| Difficulty mix | Foundation 2 · Intermediate 3 · Challenge 4 · Error redo 1 |
| Chapter | Chapter: S5 Physics | Momentum and Collisions: Conservation, Impulse and Collision Types |
| Level | S5 |
02 Questions (10 items)
- FoundationA 2 kg body at 3 m/s hits a stationary 4 kg body elastically. What is the final velocity of the 2 kg body?
- FoundationIn the same collision what is the final velocity of the 4 kg body?
- IntermediateA 3 kg body at 6 m/s hits a stationary 3 kg body elastically. What are the final velocities?
- IntermediateA 1 kg body at 8 m/s hits a stationary 3 kg body elastically. What are the final velocities?
- IntermediateA 4 kg body at 2 m/s hits a stationary 2 kg body elastically. What is the final velocity of the 2 kg body?
- ChallengeA 0.15 kg ball arrives at 8 m/s and is driven back at 20 m/s in 0.02 s. What is the average force?
- ChallengeA 1 000 kg car at 20 m/s runs into an identical car at 10 m/s and they lock together. Find the final speed and the energy lost.
- ChallengeA 5 kg body at 3 m/s collides elastically with a stationary 1 kg body. What is the total kinetic energy afterwards?
- ChallengeA 0.02 kg bullet at 400 m/s embeds itself in a stationary 1.98 kg block. What is the speed of the block?
- Error redoA student uses conservation of kinetic energy to find the common velocity in a perfectly inelastic collision. Why is that wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | Minus 1 m/s, so it rebounds at 1 m/s, from 2 minus 4 over 6 times 3. | A light body bounces back off a heavier one, the classic elastic result. |
| 2 | 2 m/s, from twice 2 over 6 times 3. | Use both elastic formulas together so the answer satisfies momentum and energy. |
| 3 | Zero and 6 m/s, the velocities simply swap. | For equal masses an elastic collision just exchanges the velocities. |
| 4 | The 1 kg rebounds at 4 m/s and the 3 kg moves at 4 m/s. | Momentum 8 and energy 32 J both balance, which is how you check the answer. |
| 5 | Eight thirds, roughly 2.67 m/s, from twice 4 over 6 times 2. | Exact fractions are fine, so do not round too early. |
| 6 | 210 N, since the change of 4.2 units divides by 0.02 s. | For a reversal add 8 and 20 to get 28 rather than subtracting. |
| 7 | 15 m/s, with kinetic energy falling from 250 000 J to 225 000 J, a loss of 25 000 J. | For a perfectly inelastic collision take the loss as the difference of the two kinetic energies. |
| 8 | 22.5 J, exactly as before the collision. | Elastic by definition means kinetic energy is conserved, so it validates your answer. |
| 9 | 4 m/s, since momentum 8 over a total mass of 2 gives 4. | A bullet staying inside the block is a perfectly inelastic collision. |
| 10 | Kinetic energy must fall in that collision, so only momentum can be used; the energy route gives a speed that is too high. | Classify the collision first, then choose which conservation law applies. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
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