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S4 Physics: Newton’s Laws of Motion Paper 4 (braking, crash safety and real use)
S4 Physics: Newton’s Laws of Motion Paper 4 (braking, crash safety and real use)
Paper 4 leaves the classroom: braking, seat belts, bouncing and towing, all tracked with F = ma and momentum.
Quick answer 4 s and 40 m; 4 m/s2; it lengthens the collision time; 15,000 N; 75 N; 13.3 m; 4,800 N; 4 m/s2 with 2,000 N; 3 m/s2; it goes with the square of the speed.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 questions |
| Suggested time | 25 minutes |
| Difficulty mix | Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1 |
| Chapter | Chapter: S4 Physics: Newton’s Laws of Motion |
| Level | S4 |
02 Questions (10 items)
- FoundationA car travels at 20 m/s and brakes at 5 m/s². Find the time and the distance to stop.
- FoundationA 1,000 kg car feels a braking force of 4,000 N. Find the deceleration.
- FoundationWhat is the main job of a seat belt in a crash?
- FoundationWhat is the weight of a 1,500 kg car, taking g as 10 m/s²?
- IntermediateA 0.15 kg ball drops 1.8 m and rebounds to 0.8 m. If contact lasts 0.02 s, find the average force, taking g as 10 m/s².
- IntermediateA driver travels at 60 km/h with a reaction time of 0.8 s. Find the reaction distance.
- IntermediateA 1,200 kg car stops from 20 m/s in 50 m. Find the average braking force.
- ChallengeA 1,000 kg car tows a 500 kg trailer with 6,000 N of net driving force. Find the acceleration and the tension on the trailer.
- ChallengeA 70 kg person on a scale in a lift reads 910 N, taking g as 10 m/s². Find the acceleration and its direction.
- Error redoA student writes that doubling the speed doubles the braking distance. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 4 s and 40 m | The time is 20 over 5, or 4 s, and the distance is 400 over 10, or 40 m. |
| 2 | 4 m/s² | The deceleration is 4,000 over 1,000, or 4 m/s2 against the motion. |
| 3 | It lengthens the slowing time and so lowers the average force on the person | For a fixed momentum change a longer time means a smaller force, and it also keeps the person inside. |
| 4 | 15,000 N | W equals mg, so 1,500 times 10 gives 15,000 N. |
| 5 | 75 N | The speeds are 6 m/s down and 4 m/s up, a change of 10 m/s, so 0.15 times 10 over 0.02 is 75 N. |
| 6 | About 13.3 m | The speed is 16.7 m/s, and multiplying by 0.8 s gives 13.3 m. |
| 7 | 4,800 N | The deceleration is 400 over 100, or 4 m/s2, and 1,200 times 4 gives 4,800 N. |
| 8 | 4 m/s² with tension 2,000 N | The pair accelerates at 4 m/s2, and the trailer needs 500 times 4, or 2,000 N, which is the drawbar tension. |
| 9 | 3 m/s² upward | The extra 210 N over the weight gives a of 3 m/s2, and a reading above the weight means upward acceleration. |
| 10 | The braking distance goes with the square of the speed, so doubling the speed makes it four times as long. | The formula shows the square, so 40 m becomes 160 m. |
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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