AS Daily A Level Physics question
A trolley jack lifts a car of weight 2000 N by 0.40 m. The user does 1200 J of work on the handle. What is the efficiency of the lift?
Answer
The correct answer is C.
Correct: C — 67%. A — 40% comes from incorrectly treating the 0.40 m lift as 40% rather than comparing energies. B — 100% assumes no losses, but the useful output is 2000 × 0.40 = 800 J, which is less than the 1200 J input. C — 67% because efficiency = 800/1200 × 100% ≈ 67%. D — 150% inverts the ratio (1200/800 × 100%), giving an impossible efficiency greater than 100%.