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P4 General Studies: Forces and Simple Machines (Paper 3 (challenge))
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P4 General Studies: Forces and Simple Machines (Paper 3 (challenge))
Paper three runs multi-step sums on balanced moments, comparing power, chained efficiencies and real pulley efforts.
Direct answers Write each step as a sum with units first, then check whether 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: P4 General Studies: Forces and Simple Machines |
| Level | parts of a closed circuit, conductors against insulators, series against parallel, adding up battery voltage, and electrical safety |
02 Questions (10 items)
- FoundationHow many newtons are there in 1.5 kN?
- FoundationAn object feels 12 N to the right and 5 N to the left. What is the net force?
- FoundationAn object is pulled 50 N to the left and 50 N to the right. What happens?
- IntermediateA lever has 60 N at 0.8 m and 40 N at 1.2 m on the other side. What happens?
- IntermediateMachine A does 900 J in 30 s and machine B does 1200 J in 50 s. Which has more power and by how much?
- IntermediateA motor takes 500 W at 60 per cent efficiency, and its output passes through pulleys at 80 per cent. What useful power comes out?
- ChallengeAn effort of 300 N along a 3 m ramp raises 600 N by 1.2 m. What is the efficiency?
- ChallengeA 240 N load is 0.3 m from the pivot and the effort point moves from 1.2 m to 1.6 m. How much does the effort drop?
- ChallengeA four-section pulley system lifts 1000 N at 90 per cent efficiency. What real effort is needed?
- Error redoError clinic: a machine can save work. True?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 1500 N. | 1 kN is 1000 N, so 1.5 times 1000 gives 1500 N. |
| 2 | 7 N to the right. | Opposite forces subtract, 12 minus 5 gives 7 N, in the direction of the larger force. |
| 3 | The net force is zero and it stays at rest or moves at constant speed. | The forces cancel, 50 minus 50 is zero, so the object does not accelerate. |
| 4 | Both moments are 48 N m, so the lever balances. | 60 times 0.8 is 48 and 40 times 1.2 is also 48, so the moments match. |
| 5 | Machine A, by 6 W. | A gives 900 over 30, that is 30 W, and B gives 1200 over 50, that is 24 W, a difference of 6 W. |
| 6 | 240 W. | 500 times 0.6 gives 300 W, times 0.8 gives 240 W, so efficiencies multiply rather than add. |
| 7 | 80.0 per cent. | Useful work is 720 J, input work is 900 J, and 720 over 900 gives 80.0 per cent. |
| 8 | From 60 N to 45 N, a drop of 15 N. | The moment stays 72 N m, so 72 over 1.2 is 60 N and 72 over 1.6 is 45 N, a drop of 15 N. |
| 9 | 277.8 N. | The ideal effort is 1000 over 4, that is 250 N, and 250 over 0.9 gives 277.8 N. |
| 10 | No. | A machine saves force or changes direction, but the input work is never less than the useful work. |
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.
Paper four clears the conductor, insulator and battery direction misconceptions.Tutor Registration →
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