A2 Daily A Level Physics question
A turntable spins steadily at a fixed rate (constant revolutions per second). A small marker at radius r casts a shadow so that its horizontal position executes SHM of amplitude r. The marker is moved to radius 2r, with the turntable’s spin rate unchanged. By what factor does the maximum acceleration of the shadow change?
Answer
The correct answer is B.
Correct: B — It doubles (×2). At fixed spin rate the angular speed is constant, so the required inward (centripetal) acceleration is directly proportional to radius; the SHM projection has maximum acceleration proportional to amplitude, so doubling radius/amplitude makes the maximum acceleration twice as large. A … Incorrect: this treats acceleration as inversely proportional to radius by mistakenly holding linear speed constant instead of angular speed. B … Correct as stated. C … Incorrect: although the period of the SHM projection is unchanged, the maximum acceleration depends on amplitude at fixed period; it does not stay the same. D … Incorrect: this over-squares the change (e.g. noticing v doubles so v² quadruples but forgetting the simultaneous doubling of r in v²/r), or wrongly assuming acceleration scales with amplitude squared.