A child sits on a rotating horizontal platform in a playground. The child moves with a constant speed along a circular path, as illustrated in [Figure 4.1]. An observer is standing a long distance away from the child. During one particular revolution, the child, moving at a speed of 7.5 m s⁻¹, starts blowing a whistle at point P and stops blowing it at point Q on the circular path. The whistle emits sound of frequency 950 Hz. The speed of sound in air is 330 m s⁻¹.

Q: What topic does this question test?

This question tests Waves in A-Level Physics (syllabus code 9702). It is worth 6 marks.

Q: Which exam paper is this question from?

This question appeared in the Cambridge A-Level Physics Feb/Mar 2017 examination, Paper 2 Variant 2 (9702_m17_qp_22.pdf).

Question

A child sits on a rotating horizontal platform in a playground. The child moves with a constant speed along a circular path, as illustrated in [Figure 4.1]. An observer is standing a long distance away from the child. During one particular revolution, the child, moving at a speed of 7.5 m s⁻¹, starts blowing a whistle at point P and stops blowing it at point Q on the circular path. The whistle emits sound of frequency 950 Hz. The speed of sound in air is 330 m s⁻¹.

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