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P4 General Studies: Forces and Simple Machines (Paper 4 (error clinic))
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P4 General Studies: Forces and Simple Machines (Paper 4 (error clinic))
Paper four revisits the five commonest mistakes, with three sums on power, efficiency and gears.
Direct answers When a sentence claims work is saved or a bigger effort means more speed, think of energy conservation and net force.
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)
- FoundationA crate is pushed with 50 N and friction is 30 N while it slides. What is the net force?
- FoundationWhat is the weight of a 5 kg dumbbell? (take g as 10 N per kg)
- FoundationA fixed pulley raises 80 N by 1 m. What effort is needed and what is the benefit?
- IntermediateHow much work lifts 200 N by 2 m, and how much when it is carried horizontally for 2 m?
- IntermediateA 90 N load is 0.6 m from the pivot and the effort arm is 1.8 m. What effort is needed?
- IntermediateMachine A does 1800 J in 60 s and machine B does 2400 J in 120 s. Which has more power and by how much?
- ChallengeA machine takes 1200 J and gives 900 J of useful work. What is its efficiency and where does the rest go?
- ChallengeA 500 N load is raised 0.8 m along a 5 m ramp at 80 per cent efficiency. What effort is used?
- ChallengeGear A has 15 teeth and drives a 45-tooth gear B. If A turns 90 times, how many turns does B make?
- Error redoError clinic: a bigger effort always means a bigger speed. True?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 20 N. | Friction opposes the push, so 50 minus 30 gives 20 N and the crate speeds up. |
| 2 | 50 N. | Weight is mass times g, so 5 times 10 gives 50 N. |
| 3 | 80 N; the benefit is pulling down to raise the load. | A fixed pulley gives no force gain, it only changes the direction of the effort. |
| 4 | 400 J vertically, and 0 J horizontally. | Lifting is force along motion, 200 times 2 gives 400 J; carrying is perpendicular, so no work. |
| 5 | 30 N. | The moment is 90 times 0.6, that is 54 N m, and 54 over 1.8 gives 30 N. |
| 6 | Machine A, by 10 W. | A gives 30 W and B gives 20 W, so the difference is 10 W. |
| 7 | 75.0 per cent, and the other 300 J becomes heat from friction. | 900 over 1200 gives 75.0 per cent, and the missing 300 J turns into heat. |
| 8 | 100 N. | Useful work is 400 J, input work is 500 J, and 500 over 5 m gives 100 N. |
| 9 | 30 turns. | Three times the teeth means a third of the speed, and 90 times 15 over 45 gives 30 turns. |
| 10 | No. | Speed changes depend on the net force and the mass; a large friction or weight can cancel a large effort. |
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.
With all four done, go back to the chapter page and revise the three parts of a closed circuit plus three safety habits.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.