A2 Daily A Level Physics question
A washing machine increases its spin rate from 1000 rpm to 1200 rpm while the drum radius stays the same. For a 0.20 kg portion of wet clothes pressed against the drum wall, by what percentage does the centripetal force on it change?
Answer
The correct answer is A.
Correct: A — Increases by 44%. With radius and mass unchanged, centripetal force is proportional to speed squared: increasing speed by 20% makes v become 1.2v, so F becomes (1.2)^2 = 1.44 times, i.e. a 44% increase. B treats the force as directly proportional to speed (linear rather than squared). C miscalculates the squared effect, incorrectly turning a 20% speed rise into a 40% force rise instead of 44%. D is wrong because the force depends on speed; changing speed changes the required centripetal force.