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S4 Physics Work, Energy and Power Practice Paper 4 | kWh Bills, Efficiency Chains and the Work-Energy Theorem – 10 Questions with Answers
S4 Physics Work, Energy and Power Practice Paper 4 | kWh Bills, Efficiency Chains and the Work-Energy Theorem – 10 Questions with Answers
The fourth set of ten work and energy questions, practising kWh and joule conversions, lamp efficiency, finding a resistance force from the work-energy theorem, the energy needed to accelerate a car and crane power, each with an answer and a one-line explanation.
Direct answers This paper has 10 questions, from W = Fs to kWh and the work-energy theorem, with g = 10 m/s^2 throughout; suggested time 25 minutes.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 25 minutes |
| Difficulty mix | Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1 |
| Chapter | S4 Physics: Work, Energy and Power |
| Level | S4 (DSE) |
02 Questions (10 items)
- FoundationA force of 12 N pushes an object 7 m in the direction of the force. How much work is done?
- FoundationA ball of mass 2 kg moves at 3 m/s. What is its kinetic energy?
- FoundationA 3 kg book is lifted from the floor to a shelf 8 m high. How much potential energy does it gain?
- FoundationA 60 W lamp is left on for 10 minutes. How much energy does it use?
- IntermediateA lamp turns only 12 J of every 60 J of electrical energy into light, the rest becoming heat. What is its efficiency?
- IntermediateA 1.5 kW electric kettle is used for 8 minutes. How much energy does it use in kWh, and what is that in joules?
- IntermediateA 5 kg stone falls freely from a height of 20 m with no air resistance. What are its kinetic energy and speed on landing?
- ChallengeA 900 kg car accelerates from 10 m/s to 20 m/s. How much extra energy is needed?
- ChallengeA 4 kg block of ice slides 16 m on ice at 8 m/s and then stops. What is the average friction force?
- Error redoA crane lifts a load 5 m at constant speed with a force of 2 000 N in 4 s. What is its power? (A common wrong answer is 500 W.)
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | W = F * s = 12 * 7 = 84 J. | The force and the displacement are in the same direction, so the values multiply directly. |
| 2 | E = 1/2 mv^2 = 1/2 * 2 * 3^2 = 9 J. | Kinetic energy is proportional to the square of the speed, so a slow object has very little of it. |
| 3 | E = mgh = 3 * 10 * 8 = 240 J. | Only the change in height counts; the path taken does not matter. |
| 4 | t = 600 s; E = 60 * 600 = 36 000 J. | Power is energy per second, so the time must be converted to seconds first. |
| 5 | Efficiency = 12 / 60 * 100% = 20%. | Efficiency is useful output divided by total input; the rest of the energy is not destroyed but becomes heat. |
| 6 | 1.5 * (8 / 60) = 0.2 kWh; 0.2 * 3 600 000 = 720 000 J (that is, 1 500 * 480). | Multiplying kW by hours gives kWh; to convert to joules, multiply by 3 600 000. |
| 7 | E = mgh = 5 * 10 * 20 = 1 000 J; v = sqrt(2 * 10 * 20) = 20 m/s. | All the potential energy becomes kinetic energy, so the speed does not depend on the mass. |
| 8 | dE = 1/2 * 900 * (20^2 – 10^2) = 1/2 * 900 * 300 = 135 000 J. | The change in kinetic energy uses the difference of the squares of the speeds, not the final speed alone. |
| 9 | Kinetic energy = 1/2 * 4 * 8^2 = 128 J; F = 128 / 16 = 8 N. | The work done against friction equals the loss in kinetic energy, divided by the sliding distance. |
| 10 | W = 2 000 * 5 = 10 000 J; P = 10 000 / 4 = 2 500 W. | Power is total work divided by time; dividing the force by the time leaves out the displacement. |
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.
