A train is moving on a straight track with speed 20 ms-1. It is blowing its whistle at the frequency of 1000 Hz. The percentage change in the frequency heard by a person standing near the track as the train passes him is close to (speed of sound = 320 ms-1)

Question

A train is moving on a straight track with speed 20 ms-1. It is blowing its whistle at the frequency of 1000 Hz. The percentage change in the frequency heard by a person standing near the track as the train passes him is close to (speed of sound = 320 ms-1) (A) 12 % (B) 6 % (C) 18 % (D) 24 %

Tardigrade Admin · Accepted Answer

f 1=1000((320/300-20))=1066 Hz f 2=1000((320/300+20))=941 Hz ∴ Change is ≃ 12 %

Q. A train is moving on a straight track with speed $20 m s^{- 1} .$ It is blowing its whistle at the frequency of $1000 Hz$ . The percentage change in the frequency heard by a person standing near the track as the train passes him is close to (speed of sound $= 320 m s^{- 1}$ )

$12%$

$6%$

$18%$

$24%$

$f_{1} = 1000 (\frac{320}{300 - 20}) = 1066 Hz$
$f_{2} = 1000 (\frac{320}{300 + 20}) = 941 Hz$
$∴$ Change is $≃ 12%$

Q. A train is moving on a straight track with speed 20ms−1. It is blowing its whistle at the frequency of 1000Hz. The percentage change in the frequency heard by a person standing near the track as the train passes him is close to (speed of sound =320ms−1)

12%

6%

18%

24%