Answer
(a) (1) moving toward.
Explanation: Frequency heard by the person is greater than the frequency of the source. This is the case when the person is moving toward a stationary source.
(b) 13.7 m/s
Work Step by Step
(a) Frequency heard by the person is greater than the frequency of the source. This is the case when the person is moving toward a stationary source. So the correct option is (1).
(b) $f_{o}=520\,Hz$, $f_{s}=500\,Hz$,
Speed of sound $v=(331+0.6T_{C})m/s=(331+0.6\times20)m/s=343\,m/s$
$f_{o}=(1+\frac{v_{o}}{v})f_{s}\implies$
$520\,Hz=(1+\frac{v_{o}}{343\,m/s})500\,Hz$
$\implies \frac{520}{500}=1.04=1+\frac{v_{o}}{343\,m/s}$
Or $0.04=\frac{v_{o}}{343\,m/s}$
Then, the person's speed $v_{o}=0.04\times343\,m/s=13.7\,m/s$
