Physics (AS & A Level) · Oct / Nov 2017 · Paper 12 · Question 22

When sound travels through air, the air particles vibrate. A graph of displacement against time for a single air particle is shown. [graph of displacement against time, showing a sinusoidal wave with period T, crossing zero at 0, T/2, T, 3T/2, 2T] Which graph best shows how the kinetic energy of the air particle varies with time?

1. A[graph: kinetic energy against time, starting at maximum at t=0, decreasing to zero at T/2, rising to maximum at T, decreasing to zero at 3T/2, rising at 2T]
2. B[graph: kinetic energy against time, starting at zero at t=0, rising to maximum at T/2, decreasing to zero at T, rising to maximum at 3T/2, decreasing to zero at 2T]
3. C[graph: kinetic energy against time, starting at maximum at t=0, with four oscillations between 0 and 2T, minima at T/4, 3T/4, 5T/4, 7T/4]
4. D[graph: kinetic energy against time, starting at zero at t=0, with four oscillations between 0 and 2T, maxima at T/4, 3T/4, 5T/4, 7T/4]

As printed in the paper