Test Index

Waves Part 1

Section: Physics

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Question : 61 of 100

Marks: +1, -0

A musician using an open flute of length 50 cm produces second harmonic sound waves. A person runs towards the musician from another end of a hall at a speed of 10 km/h. If the wave speed is 330 m/s, the frequency heard by the running person shall be close to :

[9 Jan 2019 Shift 2]

753 Hz
500 Hz
333 Hz
666 Hz

Solution:

Frequency of the sound produced by flute,

f =

2\left(\frac{v}{2l}\right)

=

\frac{2\times 330}{2\times 0.5}

= 660 Hz

Velocity of observer ,

v_0

= 10 ×

\frac{5}{18}

=

\frac{24}{9}

m/s

∴ frequency detected by observer , f' =

\left[\frac{v+v_0}{v}\right]

f

∴ f' =

\left[\frac{\frac{25}{9}+330}{330}\right]

660

= 335.56 × 2 = 671.12

∴ closest answer is (4)

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