The diagram shows a car travelling at a constant speed in a straight line between person P and person Q from point X to point Y. [Figure 24.1] The car sounds its horn continuously as it travels. The horn emits sound of constant frequency. Which statements about what person P and person Q hear during the motion of the car are correct? 1 Person P hears a sound of increasing frequency. 2 Person Q hears a sound of decreasing frequency. 3 Person Q always hears a sound of higher frequency than person P.

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