A bus moving with an uniform speed of 72 km / h towards a building blows a horn of frequency 1.7 KHz. If speed of sound in air is 340 m / s, what will be the frequency of echo heard by bus driver?

Question

A bus moving with an uniform speed of 72 km / h towards a building blows a horn of frequency 1.7 KHz. If speed of sound in air is 340 m / s, what will be the frequency of echo heard by bus driver? (A) 1.8 KHz (B) 2.0 KHz (C) 1.6 KHz (D) 1.4 KHz

Tardigrade Admin · Accepted Answer

According to Doppler's effect,
Observed frequency of sound reflected from building is given by

f^{'} = f (\frac{v + v _{b}}{v - v _{b}}) \dots .

(i)
Here,

v =

speed of sound

= 340 m / s

v_{b} =

speed of bus

= 7.2 km / h = 20 m s^{- 1}

and

f =

original frequency produced by horn

= 1.7 k Hz

Hence, putting these value in Eq. (i),
we get Observed frequency by bus driver,
Hence, putting these value in Eq. (i),
we get Observed frequency by bus driver,

f^{'} = 1.7 (\frac{340 + 20}{340 - 20})

= 1.9125 k Hz \approx 1.8 k Hz

Q. A bus moving with an uniform speed of $72 km / h$ towards a building blows a horn of frequency $1.7 KHz$ . If speed of sound in air is $340 m / s$ , what will be the frequency of echo heard by bus driver?

$1.8 KHz$

$2.0 KHz$

$1.6 KHz$

$1.4 KHz$

Q. A bus moving with an uniform speed of 72km/h towards a building blows a horn of frequency 1.7KHz. If speed of sound in air is 340m/s, what will be the frequency of echo heard by bus driver?

1.8KHz

2.0KHz

1.6KHz

1.4KHz

Q. A bus moving with an uniform speed of $72 km / h$ towards a building blows a horn of frequency $1.7 KHz$ . If speed of sound in air is $340 m / s$ , what will be the frequency of echo heard by bus driver?

$1.8 KHz$

$2.0 KHz$

$1.6 KHz$

$1.4 KHz$