A2 Daily A Level Physics question
A small lab centrifuge spins sample tubes at a fixed radius. The angular speed is increased by 20% while the radius and sample mass remain the same. What happens to the inward (centripetal) force on a sample?
Answer
The correct answer is A.
Correct: A — increases by 44%. With mass and radius fixed, the required inward force scales with the square of angular speed, so a 1.2× increase gives 1.2² = 1.44×, i.e. a 44% increase. A uses the correct square dependence on angular speed. B assumes a linear dependence on angular speed, giving only a 20% increase. C miscalculates the square of 1.2, taking it as 1.36 instead of 1.44. D ignores that changing speed changes the required inward force; it would stay the same only if angular speed were unchanged.