A) 340 m/s
B) 170 m/s
C) 85 m/s
D) 310 m/s
Correct Answer: C
Solution :
When source is moving towards stationary observer, its apparent frequency \[{{n}_{1}}=n\left( \frac{\upsilon }{\upsilon -{{\upsilon }_{s}}} \right)\] where, \[\upsilon \to \]velocity of sound \[{{\upsilon }_{s}}\to \]velocity of source When source is moving away from observer, its apparent frequency \[{{n}_{2}}=n\left( \frac{\upsilon }{\upsilon +{{\upsilon }_{s}}} \right)\] \[\therefore \] \[\frac{{{n}_{1}}}{{{n}_{2}}}=\left( \frac{\upsilon }{\upsilon +{{\upsilon }_{s}}} \right)\times \left( \frac{\upsilon +{{\upsilon }_{s}}}{\upsilon } \right)\] \[\frac{5}{3}=\frac{\upsilon +{{\upsilon }_{s}}}{\upsilon -{{\upsilon }_{s}}}\] By solving, \[{{\upsilon }_{s}}=\frac{\upsilon }{4}=\frac{340}{4}\] \[=85m/s\]
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