Question:
A train standing at the outer signal of a railway station blows a whistle of frequency $400 \,Hz$ in still air. The train begins to move with a speed of $30\, m\, s^{-1}$ towards the platform. The frequency of the sound heard by an observer standing on the platform is
(Speed of sound in air = $330\,m \, s^{-1})$
A train standing at the outer signal of a railway station blows a whistle of frequency $400 \,Hz$ in still air. The train begins to move with a speed of $30\, m\, s^{-1}$ towards the platform. The frequency of the sound heard by an observer standing on the platform is
(Speed of sound in air = $330\,m \, s^{-1})$
Updated On: Jul 6, 2022
- $420\, Hz$
- $430\, Hz$
- $440 \, Hz$
- $450 \, Hz$
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The Correct Option is C
Solution and Explanation
Here, Frequency of source, $\upsilon=400\, Hz$
Speed of sound, $v = 330 \, m \, s^{-1}$
Speed of source (i.e. train), $\upsilon_{s}=30\, m\,s^{-1}$
As the source is moving towards stationary observer
$\therefore \upsilon' =\frac{\upsilon v}{v-v_{s}}=\frac{\left(400\,Hz\right)\times\left(330\,m\,s^{-1}\right)}{330\,m\,s^{-1}-30\,m\,s^{-1}}$
$=440\,Hz$
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Concepts Used:
Waves
Waves are a disturbance through which the energy travels from one point to another. Most acquainted are surface waves that tour on the water, but sound, mild, and the movement of subatomic particles all exhibit wavelike properties. inside the most effective waves, the disturbance oscillates periodically (see periodic movement) with a set frequency and wavelength.
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Transverse Waves -
Waves in which the medium moves at right angles to the direction of the wave.
Examples of transverse waves:
- Water waves (ripples of gravity waves, not sound through water)
- Light waves
- S-wave earthquake waves
- Stringed instruments
- Torsion wave
The high point of a transverse wave is a crest. The low part is a trough.
Longitudinal Wave -
A longitudinal wave has the movement of the particles in the medium in the same dimension as the direction of movement of the wave.
Examples of longitudinal waves:
- Sound waves
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