A2 Daily A Level Physics question
In a lab, a glider attached to a spring oscillates with small amplitude on a near-frictionless air track. A data logger flags the instants when the glider’s kinetic energy equals the elastic potential energy. The measured time between successive such instants is 0.50 s. Assuming negligible damping, which statement must be true?
Answer
The correct answer is C.
Correct: C — The period is 2.0 s. In SHM the instants when kinetic and elastic potential energies are equal occur four times per cycle (at |x| = A/√2), so the time between successive such instants is T/4; hence T = 4 × 0.50 s = 2.0 s. A treats the measured interval as a full cycle, but it is only one quarter of a cycle. B assumes the interval is half a cycle (T/2), which would make T = 1.0 s, but KE = PE occurs four times per cycle, not twice. C is correct as shown. D overestimates the period by assuming too many such events per cycle or miscounting phase intervals.