Question

two cars are moving with speed 90km/h and 36 km/h in opposite directions along a straight road the faster car horns a whistle of frequency 240Hz calculate the apparent frequency heard by a listener in slower car when they a) approach each other b) receds each other
​

Answer 1

Explanation:

ANSWER

f_1 = 400 Hzf

1

=400Hz

V_s = 340 m/sV

s

=340m/s

when both source and obsemer are moving

towards each other

f_2 = \left(\dfrac{V_s+V_2}{V_s-V_1}\right)f_1f

2

=(

V

s

−V

1

V

s

+V

2

)f

1

=\dfrac{340 + 16.5}{340-22}\times 400 = \dfrac{356.5}{318}\times 400=

340−22

340+16.5

×400=

318

356.5

×400

\cong 448Hz≅448Hz

Answer 2

Apparent frequency heard by a listener is 251.42 Hz .

Given :

Speed of source , $v_s=90 \ km/h=25\ m/s.$

Speed of receiver ,  $v_r=36\ km/h=10\ m/s .$

Frequency of whistle , f = 240 Hz .

Velocity of sound , v = 340 m/s .

We know , apparent frequency heard by a listener when they are approaching is :

$f'=(\dfrac{v-v_r}{v-v_s})f\\\\f'=(\dfrac{340-10}{340-25})\times 240\\\\f'=251.42\ Hz.$

Hence, this is the required solution.

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Doppler's Effect

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