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S4 Physics Work, Energy and Power Practice Paper 2 | Conservation of Energy, Work against Friction and Efficiency – 10 Questions with Answers
S4 Physics Work, Energy and Power Practice Paper 2 | Conservation of Energy, Work against Friction and Efficiency – 10 Questions with Answers
The second set of ten work and energy questions, practising conservation of energy, work against friction, sliding down a slope and efficiency, each with an answer and a one-line explanation.
Direct answers This paper has 10 questions, all solvable in one step with conservation of energy or W = Fs; suggested time 25 minutes.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 25 minutes |
| Difficulty mix | Foundation 3 · Intermediate 4 · Challenge 2 · Error redo 1 |
| Chapter | S4 Physics: Work, Energy and Power |
| Level | S4 (DSE) |
02 Questions (10 items)
- FoundationA box is pushed 5 m along a horizontal floor by a horizontal force of 40 N. How much work is done?
- FoundationA ball of mass 4 kg moves at 5 m/s. What is its kinetic energy?
- FoundationA 3 kg book is lifted from the floor to a shelf 4 m high. How much gravitational potential energy does it gain?
- IntermediateA hoist does 900 J of work in 30 s. What is its power?
- IntermediateA machine takes in 500 J and gives out 250 J of useful work. What is its efficiency?
- IntermediateA 2 kg object slides down from a height of 5 m and reaches the ground at 8 m/s. How much energy is lost?
- IntermediateA 30 kg sandbag is lifted 4 m in 20 s. Find the work done and the power.
- ChallengeA 4 kg object falls from a height of 10 m, losing 100 J to air resistance on the way. Find its landing speed.
- ChallengeA 5 kg block slides down a frictionless slope 3 m long and 1.2 m high. Find the potential energy lost and the final speed.
- Error redoA student says ‘a power of 500 W means 500 J of work has been done in total’. What is wrong with this?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | W = Fs = 40 * 5 = 200 J. | W = Fs applies because the force and the displacement are in the same direction. |
| 2 | KE = 1/2 mv^2 = 1/2 * 4 * 5^2 = 50 J. | Kinetic energy is proportional to the square of the speed. |
| 3 | PE = mgh = 3 * 10 * 4 = 120 J. | Take g = 10 m/s^2. |
| 4 | P = W / t = 900 / 30 = 30 W. | The unit of power is the watt, which is one joule per second. |
| 5 | Efficiency = 250 / 500 * 100% = 50%. | Efficiency is always less than 100%. |
| 6 | Initial potential energy 100 J, final kinetic energy 64 J, so 36 J is lost (as heat and sound). | With friction, potential energy does not all become kinetic energy. |
| 7 | W = 30 * 10 * 4 = 1 200 J; P = 1 200 / 20 = 60 W. | Work out the work first, then divide by the time. |
| 8 | 1/2 mv^2 = 4 * 10 * 10 – 100 = 300 J, so v = sqrt(300 * 2 / 4) = approx. 12.2 m/s. | Use conservation of energy: potential energy minus the work done against resistance equals the final kinetic energy. |
| 9 | Loss in potential energy = 5 * 10 * 1.2 = 60 J; v = sqrt(2 * 10 * 1.2) = approx. 4.9 m/s. | Without friction the final speed depends only on the height, not on the length of the slope. |
| 10 | 500 W means 500 J of work is done every second; the total work depends on how many seconds pass, W = Pt. | Power is a rate, not a total amount. |
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.
Read the S4 Physics: Work, Energy and Power chapter notes first, then work through all ten questions and mark them against the answers.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.
