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A factory siren of 560 Hz is fixed on a tower…

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

A factory siren of $560\ \text{Hz}$ is fixed on a tower. A cyclist rides straight towards it at $8.0\ \text{m/s}$ , passes the tower and rides on at the same speed. What frequency does the cyclist hear (a) before passing the tower and (b) after passing it?

Need a reminder? The key ideaShow

With the source and listener moving along the line between them, speeds measured in the air:

\displaystyle f' = f\,\frac{v \pm v_o}{v \mp v_s}

Upper signs when that body moves towards the other. An echo from a reflector coming towards you at $u$ : $f\,\dfrac{v + u}{v - u}$ .

The worked solution

Have you tried it?

Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, compare your working with the solution.

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