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S4 Physics Work, Energy and Power Practice Paper 3 | Work against Friction, Efficiency and Stair-climbing Power – 10 Questions with Answers
S4 Physics Work, Energy and Power Practice Paper 3 | Work against Friction, Efficiency and Stair-climbing Power – 10 Questions with Answers
The third set of ten work and energy questions, practising work against friction, mechanical efficiency, stair-climbing power, appliance energy use and conservation of energy, each with an answer and a one-line explanation.
Direct answers This paper has 10 questions, from W = Fs to efficiency and power, 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 3 · Intermediate 4 · Challenge 2 · Error redo 1 |
| Chapter | S4 Physics: Work, Energy and Power |
| Level | S4 (DSE) |
02 Questions (10 items)
- FoundationA force of 25 N pushes a box 8 m. How much work is done?
- FoundationA ball of mass 3 kg moves at 4 m/s. What is its kinetic energy?
- FoundationA 4 kg object is raised 5 m. How much potential energy does it gain?
- IntermediateA machine does 900 J of work in 15 s. What is its power?
- IntermediateA motor takes in 400 J and only 320 J becomes useful work. What is its efficiency?
- IntermediateA ball of mass 2 kg slides down from a height of 5 m, friction neglected. What are its speed and kinetic energy at the ground?
- IntermediateA 2 kg block of ice slides 20 m on ice at 10 m/s and then stops. What is the friction force?
- ChallengeA student of mass 60 kg runs up 20 steps, each 0.2 m high, in 20 s. What is the power?
- ChallengeA crane lifts a load 6 m at constant speed with a force of 500 N in 10 s. What is its power?
- Error redoA 100 W lamp is left on for 5 minutes. How much energy does it use? (A common wrong answer is 500 J.)
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | W = F * s = 25 * 8 = 200 J. | When the force and the displacement are in the same direction, the work equals force times distance. |
| 2 | E = 1/2 mv^2 = 1/2 * 3 * 4^2 = 24 J. | Kinetic energy is proportional to the square of the speed, so doubling the speed quadruples it. |
| 3 | E = mgh = 4 * 10 * 5 = 200 J. | Potential energy depends only on mass, g and the change in height. |
| 4 | P = W / t = 900 / 15 = 60 W. | Power is the rate of doing work, measured in watts (J/s). |
| 5 | Efficiency = 320 / 400 * 100% = 80%. | Efficiency is always below 100%, with the rest becoming heat or sound. |
| 6 | 1/2 mv^2 = mgh, so v = sqrt(2 * 10 * 5) = 10 m/s; E = 1/2 * 2 * 10^2 = 100 J. | When all the potential energy becomes kinetic energy the mass cancels, so the speed does not depend on the mass. |
| 7 | Kinetic energy lost = 1/2 * 2 * 10^2 = 100 J; F = 100 / 20 = 5 N. | The work done against friction equals the loss in kinetic energy, divided by the sliding distance. |
| 8 | h = 20 * 0.2 = 4 m; W = 60 * 10 * 4 = 2 400 J; P = 2 400 / 20 = 120 W. | Find the total height first, then the work, then divide by the time. |
| 9 | W = 500 * 6 = 3 000 J; P = 3 000 / 10 = 300 W. | At constant speed the lifting force equals the weight, so P = Fv gives the same result. |
| 10 | t = 5 * 60 = 300 s; E = P * t = 100 * 300 = 30 000 J. | Power is quoted per second, so the time must be converted to seconds first. |
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.
