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S5 Physics: Momentum and Collisions – Error-Correction Practice (10 Questions)
S5 Physics: Momentum and Collisions – Error-Correction Practice (10 Questions)
Ten items target the usual slips: a missing direction, weight used as mass, a rebound speed not reversed, energy conservation misused, and signs ignored for opposite motions.
Quick answer 1. 12 kg m/s east; 2. 5 m/s; 3. 15 kg m/s; 4. 7 kg m/s; 5. 140 N; 6. 6 m/s east; 7. 1.2 m/s and 5.4 J lost; 8. 300 N; 9. momentum only; 10. 2 kg m/s east.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 questions |
| Suggested time | about 20 minutes |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 2 · Error redo 2 |
| Chapter | Chapter: S5 Physics | Momentum and Collisions: Conservation, Impulse and Collision Types |
| Level | S5 |
02 Questions (10 items)
- FoundationA 3 kg ball rolls east at 4 m/s. What is its momentum?
- FoundationA stationary 2 kg box is pushed by 25 N for 0.4 s. What is its final speed?
- FoundationA ball weighing 50 N rolls at 3 m/s. What is its momentum?
- IntermediateA 0.5 kg ball hits a wall at 8 m/s and bounces back at 6 m/s. What is the size of its momentum change?
- IntermediateFor the same ball the contact time is 0.05 s. What average force does the wall give?
- IntermediateA 4 kg cart at 5 m/s east hits a 2 kg cart moving east at 2 m/s. After the hit the 4 kg cart is at 3 m/s; find the 2 kg cart speed.
- ChallengeA 2 kg ball at 3 m/s sticks to a stationary 3 kg ball. Find the common speed and the kinetic energy lost.
- ChallengeA 1 kg ball is dropped from 0.8 m and rebounds to 0.2 m, contact time 0.02 s. Find the average force.
- Error redoA student claims kinetic energy conservation also works for inelastic collisions. What is wrong?
- Error redoA 2 kg ball moves east at 4 m/s and a 3 kg ball moves west at 2 m/s. What is the total momentum?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 12 kg m/s directed east. | Momentum is a vector, so quoting 12 without a direction loses the mark. |
| 2 | The impulse is 10 N s, so the speed is 5 m/s. | Multiply force by time for impulse, then divide by mass for speed. |
| 3 | 15 kg m/s, because 50 N is 5 kg and 5 times 3 is 15. | Convert weight to mass with g equal to 10 N/kg first; using 50 directly is ten times too big. |
| 4 | 7 kg m/s, since the reversals add as 3 plus 4. | The velocity flips sign on the rebound, so the two sizes are added. |
| 5 | 140 N, from 7 divided by 0.05. | Average force is the momentum change divided by contact time. |
| 6 | 6 m/s east, because 24 equals 12 plus twice the unknown speed. | Write total momentum before and after, then solve the equation. |
| 7 | 1.2 m/s, with 5.4 J of kinetic energy lost. | Add the masses after sticking, then subtract final from initial kinetic energy. |
| 8 | 300 N, since the speeds are 4 and 2 m/s and the momentum change is 6. | Get each speed from the square root of twice g h; opposite directions add. |
| 9 | Some kinetic energy becomes heat and deformation, so only momentum is conserved. | Momentum is conserved in every collision, kinetic energy only in elastic ones. |
| 10 | 2 kg m/s east, because 8 minus 6 is 2. | Fix a positive direction first and give opposite motions opposite signs. |
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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