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A boy riding on his bike is going toward...

A boy riding on his bike is going towards east at a speed of `4sqrt2ms^-1`. At a certain point he produces a sound pulse of frequency 1650 Hz that travels in air at a speed of `334 m s^-1` . A second boy stands on the ground `45^@` south of east from him. Find the frequency of the pulse as received by the second boy.

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The correct Answer is:
A
`u=334 /s`
`v_b=4/2m/s, v_0=0`
So, `v_s=v_bcostheta`
`=4xxsqrt2xx(1/sqrt2)=4m/s`
So, the apparent frequency
`f=((u++)/(u-v_bcostheta))f`
`=(334/(334-4))xx1650=1670Hz`
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