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# Find the frequency heard by the observer if velocity of observer = 15 m/s, velocity of source = 20 m/s, frequency of sound source = 400 Hz and velocity of sound waves = 340 Hz

$(a)\;418\;Hz\qquad(b)\;408\;Hz\qquad(c)\;438\;Hz\qquad(d)\;428\;Hz$

Can you answer this question?

Answer : (d) $\;428\;Hz$ Explanation : Have to find the component of velocity of source and observer along the line joining both of them$f^{'}=(\large\frac{v+v_{0} cos 30^{0}}{v-v_{s}cos 60^{0}})\;f^{'}=(\large\frac{340 + 15 \times \large\frac{\sqrt{3}}{2}}{340-20\times \large\frac{1}{2}}) \times 400$$=427.86$$=428 (app)\;Hz$
answered Mar 10, 2014 by
edited Mar 10, 2014 by yamini.v