SATHEE: Waves - Result Question 72

Waves - Result Question 72

74. A train moving at a speed of $220 m s^{- 1}$ towards a stationary object, emits a sound of frequency $1000 H z$ . Some of the sound reaching the object gets reflected back to the train as echo. The frequency of the echo as detected by the driver of the train is :

[2012M]

(speed of sound in air is $330 m s^{- 1}$ )

(a) $3500 H z$

(b) $4000 H z$

(d) $3000 H z$

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Answer:

Correct Answer: 74. (c)

Solution:

(According to Doppler effect in sound)

$f^{'} = (\frac{v + u}{v - u}) f$

where $f =$ original frequency of source of sound $f^{'} =$ Apparent frequency of source because of the relative motion between source and observer.

$f^{'} = (\frac{330 + 220}{330 - 220}) 1000 = 5000 H z$

Velocity of sound direction is always taken from source to observer. All the velocities in the direction of $v$ are positive and in the opposite direction of $v$ are taken negative.

Waves - Result Question 72

74. A train moving at a speed of $220 m s^{- 1}$ towards a stationary object, emits a sound of frequency $1000 H z$ . Some of the sound reaching the object gets reflected back to the train as echo. The frequency of the echo as detected by the driver of the train is :

Answer:

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Waves - Result Question 72

74. A train moving at a speed of 220ms−1 towards a stationary object, emits a sound of frequency 1000Hz. Some of the sound reaching the object gets reflected back to the train as echo. The frequency of the echo as detected by the driver of the train is :

Answer:

Engineering Preparation

Medical Preparation

NCERT Books & Solutions

Important Resources

Other Resources

Syllabus

Test Platform

Sample Mock Test

Mentorship

NCERT Exercise Video Solution

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74. A train moving at a speed of $220 m s^{- 1}$ towards a stationary object, emits a sound of frequency $1000 H z$ . Some of the sound reaching the object gets reflected back to the train as echo. The frequency of the echo as detected by the driver of the train is :