1
You visited us 1 times! Enjoying our articles? Unlock Full Access!
Question

A train approaching a crossing X at a speed 40 m/s sounds a horn of frequency 620 Hz, when it is at a distance of 30 m from the crossing. Speed of sound in air is 334 m/s. What is the frequency heard by an observer (at rest) who is at a perpendicular distance of 40 m from the crossing on the straight road. [Assume, medium is stationary]

A
620 Hz
No worries! We‘ve got your back. Try BYJU‘S free classes today!
B
310 Hz
No worries! We‘ve got your back. Try BYJU‘S free classes today!
C
688 Hz
No worries! We‘ve got your back. Try BYJU‘S free classes today!
D
668 Hz
Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses
Open in App
Solution

The correct option is D 668 Hz From the figure, we deduce that, cosθ=3050=35 Given that, Actual frequency (f0)=620 Hz Velocity of source (vs)=40 m/s Velocity of observer (vo)=0 Velocity of sound in a stationary medium (v)=334 m/s Let fapp be the apparent frequency heard by observer. From Doppler effect, we can write that, fapp=f0(v±vov±vs) ⇒fapp=f(vv−vscosθ) [(-) ve sign is because source approaching the observer and we take the component of velocity along the line joining source and observer] Substituting the given data, we get fapp=620⎛⎜ ⎜ ⎜⎝334334−40×35⎞⎟ ⎟ ⎟⎠=620×334310=668 Hz

Suggest Corrections
0
Join BYJU'S Learning Program
Related Videos
Standing Longitudinal Waves
PHYSICS
Watch in App
Explore more
Join BYJU'S Learning Program