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S3 Science: Forces, Motion, Speed-Time Graphs and Net Force (Paper 3: challenge)
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S3 Science: Forces, Motion, Speed-Time Graphs and Net Force (Paper 3: challenge)
The third paper handles multi-stage trips, pursuit and braking, and has the longest working of the set.
Direct answers Keep the unit beside every step and finish by checking that the size of the answer is sensible.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 20 |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1 |
| Chapter | Chapter: S3 Science: Forces, Motion, Speed-Time Graphs and Net Force |
| Level | S3 Science |
02 Questions (10 items)
- FoundationA car runs 2 hours at 60 km/h then 3 hours at 80 km/h. What is the average speed?
- FoundationWhat is the weight of a 5 kg object on Earth, taking g as 10 N/kg?
- FoundationForces of 6 N and 8 N act at right angles. What is the resultant?
- IntermediateA car at 20 m/s brakes at 4 m/s². How long until it stops?
- IntermediateA 3 kg object is pulled with 30 N against 6 N of friction. What is its acceleration?
- IntermediateOn a distance-time graph, 12 metres are covered in the first 4 seconds and 6 metres in the next 6. What is the second speed?
- ChallengeA leaves at 5 m/s twenty seconds before B follows at 7 m/s. How long does B take to catch up?
- ChallengeA car at 10 m/s brakes at 2 m/s². What is the stopping distance?
- ChallengeA 60 kg person stands in a lift accelerating upward at 2 m/s². What is the normal force from the floor, taking g as 10 N/kg?
- Error redoA student reports the average of 60 km/h for 2 hours and 80 km/h for 3 hours as 70 km/h. What is the correct value?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 72 km/h | The total is 120 plus 240 kilometres over 5 hours, and 360 divided by 5 gives 72. |
| 2 | 50 N | Weight is mass times gravitational field strength, so 5 times 10 is 50 newtons while the mass stays 5 kg. |
| 3 | 10 N | Perpendicular forces combine by Pythagoras, and the square root of 36 plus 64 is 10. |
| 4 | 5 seconds | Time is the change in speed over the acceleration, so 20 over 4 is 5 seconds. |
| 5 | 8 m/s² | The net force is 30 minus 6, and 24 over 3 gives 8. |
| 6 | 1 m/s | The second part gives 6 over 6 as 1 m/s while the first was 12 over 4 as 3 m/s, so the slopes differ. |
| 7 | 50 seconds | A leads by 100 metres and the relative speed is 2 m/s, so 100 divided by 2 is 50 seconds. |
| 8 | 25 m | The stopping distance is the square of the speed over twice the acceleration, so 100 over 4 is 25 metres. |
| 9 | 720 N | The floor supports the weight and supplies the acceleration, so 60 times 12 is 720 newtons. |
| 10 | 72 km/h | The two stages last different times, so average the totals instead: 360 kilometres over 5 hours gives 72. |
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.
The challenge paper takes on multi-stage trips and pursuit: add the distances segment by segment, use relative speed for pursuit, square the speed over twice the acceleration for braking, and remember weight is mg while mass stays fixed.Tutor Registration →
Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.