A train, standing in a station yard, blows a whistle of frequency… - Vidyadip

MCQ

A train, standing in a station yard, blows a whistle of frequency $400Hz$ in still air. The wind starts blowing in the direction from the yard to the station with a speed of $10\ m/ s$. Given that the speed of sound in still air is $340\ m/ s,$

A
The frequency of sound as heard by an observer standing on the platform is $400Hz.$
B
The speed of sound for the observer standing on the platform is $350\ m/ s.$
✓
Both $A$ and $B$
D
The frequency of sound as heard by the observer standing on the platform will decrease.

✓

Answer

Correct option: C.

Both $A$ and $B$

As the disatance between listener and source does not change so frequency of sound does not change the as heard listener. i.e.,he heard $\text{v}_0=400\text{Hz}.$ verifies option $(a)$
$\text{v}_0=400\text{Hz}$ frequency of source of sound.
Velocity of wind $\text{v}_\text{w}=10\text{m/ s}$ from source of listenr.
Speed of sound in still air $= \text{v}_\text{s}=340\ \text{m/ s}$
As the listenner is standing on platfrom.
Speed od sound with respect to listener $\text{v}_\text{s}+\text{v}_\text{w}=340+10=350\ \text{m/ s}$
Verifies the option $(b)$
Reject the $(d)$ as it constant $\text{v}_0=400\text{Hz}$

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