Question

The frequency of the sound of a car horn as received by an observer towards whom the car is moving differs from the frequency of the horn by $2.0\%.$ Assuming that the velocity of sound of air is $350{\text{ms}}^{-1}$, the velocity of car is

• A. $6.0{\text{ms}}^{-1}$
• B. $7.5{\text{ms}}^{-1}$
• C. $7{\text{ms}}^{-1}$
• D. $8.5{\text{ms}}^{-1}$

Answer 1

The correct option is C $7{\text{ms}}^{-1}$

$n^{\prime }=\frac{V}{V-V_s}{n}_0$, we are given $\frac{n^{\prime }}{n_0}=1.02$

$\frac{350}{350-V_s}=1.02$,

$V_s=6.86m{s}^{-1}=7m{s}^{-1}\left(approx\right)$