A2 Daily A Level Physics question
A small glider on an air track is attached to a horizontal spring and oscillates with amplitude 0.10 m in simple harmonic motion. Ignoring friction, when its displacement is 0.050 m from equilibrium, what percentage of the total mechanical energy is kinetic?
Answer
The correct answer is A.
Correct: A — 75%. In SHM the spring’s potential energy depends on displacement squared, so the potential-energy fraction at x is (x/A)^2 = (0.05/0.10)^2 = 0.25; the kinetic fraction is 1 − 0.25 = 0.75 = 75%. A is correct because it uses the squared dependence to find the remaining energy is kinetic. B is wrong because it assumes a linear 50% split from halving the displacement, ignoring the squared relation. C is wrong because 25% is the potential-energy fraction at that position, not the kinetic fraction. D is wrong because kinetic energy is zero only at the extremes (x = ±A), not at x = A/2.