How should error drills be used?

Redo each item yourself, then check, and write down the step that went wrong, such as a missing cos(theta) or minutes used as seconds.

Why unify units first?

Power times time gives energy, so time must be in seconds and power in watts, or the answer is out by tens of times.

S4 Physics work, energy and power paper 4: ten common slips

2026-11-10

Tutor Prep Guide · S4 Physics Work, Energy and Power

All ten items are rewritten from the most common slips; redo each one before checking.

Direct answers　Items 01 to 03 retry formulas and angles, 04 to 06 power, efficiency and units, 07 to 09 multi-step work, and 10 targets time units.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	25
Difficulty mix	Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1
Chapter	Chapter: S4 Physics Work, Energy and Power
Level	S4

02　Questions (10 items)

FoundationA 20 N force at 60 degrees to the horizontal pushes a box 5 m along level ground. Find the work done.
FoundationA 2 kg ball moves at 4 m/s. Find its kinetic energy. If the speed doubles, how many times larger is it?
FoundationA 3 kg bag is lifted 5 m. Find the gain in gravitational potential energy (g = 10 N/kg).
IntermediateA machine does 600 J of work in 4 s. Find its power.
IntermediateA machine takes in 500 J and gives 350 J of useful output. Find its efficiency.
IntermediateAn appliance rated 1.2 kW runs for 30 s. Find the energy used, in kJ.
ChallengeAn 800 kg car speeds up from 5 m/s to 15 m/s over 100 m. Find the gain in kinetic energy and the average net force.
ChallengeA 1200 kg car travelling at 20 m/s brakes with a force of 4000 N. Find the braking distance.
ChallengeA 0.5 kg ball falls freely from 20 m. Find its landing speed (g = 10 N/kg, no air resistance).
Error redoA pupil writes the energy of a 500 W machine running for 2 minutes as 1000 J. What is wrong?

03　Answers and one-line notes

#	Answer	One-line note
1	50 J	W = Fs cos(theta) = 20 x 5 x 0.5 = 50 J; an angled force must include cos(theta).
2	16 J; 4 times	Kinetic energy = 1/2 x 2 x 4 squared = 16 J, and it goes with the square of speed, so doubling speed gives 4 times.
3	150 J	Gravitational potential energy = mgh = 3 x 10 x 5 = 150 J; only the height change matters.
4	150 W	P = W / t = 600 / 4 = 150 W; joules and watts are different quantities.
5	70%	Efficiency = useful output / input = 350 / 500 = 0.7, that is 70%.
6	36 kJ	E = Pt = 1200 x 30 = 36000 J = 36 kJ; time must be in seconds.
7	80000 J; 800 N	Gain = 1/2 x 800 x (15 squared – 5 squared) = 80000 J; divide by 100 m for the net force.
8	60 m	The kinetic energy of 240000 J is removed by the braking force, so 240000 / 4000 = 60 m.
9	20 m/s	v = square root of 2 x 10 x 20 = square root of 400 = 20 m/s, independent of mass.
10	Time must be in seconds: 2 minutes = 120 s, so the energy is 500 x 120 = 60000 J.	Using minutes underestimates by a factor of 60; convert the time 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.

Book a Physics tutor 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.