question_answer

A train approaching a railway stations crossing at a speed of 120 km/h sounds a short whistle at frequency 640 Hz when it is 300m away from the crossing. The speed of sound in air is 340 m/s what will be the frequency heard by person standing on a road perpendicular to track through the crossing at a distance of 400 m from the crossing -

A) 640 Hz             

B) 680 Hz

C) 380 Hz             

D)        None of these

Correct Answer: B

Solution :

[b] \[f'=\frac{V}{V-u\cos \theta }f=680\text{ }Hz\]