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# The sound source of frequency 400 Hz is moving towards as stationary observer with a velocity of 40 m/s . The frequency heard by the observer is (The speed of sound in medium is 340 Hz .)

$(a)\;433\;Hz\qquad(b)\;453\;Hz\qquad(c)\;483\;Hz\qquad(d)\;383\;Hz$

Can you answer this question?

Answer : (b) $\;453\;Hz$
Explanation :
By Doppler's effect
$f^{|}=(\large\frac{v}{v-v_{s}})\;f$
$v\;$ - velocity of sound
$v_{s}\;$ - velocity of source
$f^{|}=\large\frac{340}{340-40}\times400=\large\frac{340}{300} \times 400$
$=453\;Hz\;.$
answered Mar 8, 2014 by