JEE PHYSICS MCQ: WAVES

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A train approaching a platform at a speed of

54 \mathrm{~km} / \mathrm{h}

sounds a whistle. An observer on the platform finds its frequency to be

1620 \mathrm{~Hz}

. The train passes the platform keeping the whistle on and without slowing down. What frequency will the observer hear after the train has crossed the platfrom? The speed of sound in air

=332 \mathrm{~m} / \mathrm{s}

View answer and explanation

Correct option: A

1480 Hz

Option A (1480 Hz) is correct because it is calculated using the Doppler effect formula for the frequency heard after the train has passed.

More Questions from WAVES

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The source of sound generating a frequency of

3\,\,kHz

reaches an observer with a speed of

0.5

times, the velocity of sound in air. The frequency heard by the observer is A source of sound emits waves with frequency

f\mathrm{ }Hz

and speed

V\mathrm{ }m/sec

. Two observers move away from this source in opposite directions each with a speed

0.2\,\,V

relative to the source. The ratio of frequencies heard by the two observers will be Assertion: The wave function of a pulse is given by

y = \frac{3}{{{{\left( {2x + 3t} \right)}^2} + 4}},

it propagates in

(– \mathrm{ve}) \,x

-direction.
Reason: The given wave function is of the form

y = f(kx +\omega t),

which represent a wave travelling in negative

X

-direction. In the fundamental mode, time taken by the wave to reach the closed end of the air filled pipe is

0.01\,\,s

. the fundamental frequency is A rope

5 \mathrm{~m}

long has a total mass of

245 \mathrm{~g}

. It is stretched with a constant tension of

1 \mathrm{~kg}

wt. If it is fixed at one end and shaken by hand at the other end, what frequency of shaking will make it break up into three vibrating segments? Take

g=980 \mathrm{~cm} \mathrm{~s}^{-2}

. If

T

is the reverberation time of an auditorium of volume

V

then