• # question_answer A person feels 2.5% difference of frequency of a motorcar horn. If the motorcar is moving to the person and the velocity of sound is 320 m/s, then the velocity of car will be A)  8 m/s (approx)            B)  800 m/s           C)  7 m/s              D)  6 m/s (approx)

By Doppler's formula $\phi '$ $\tan \,\phi =\frac{V}{{{H}^{.}}}=\frac{V}{H\,\cos \,\theta }$  $\frac{\tan \,\phi '}{\tan \,\phi }=\frac{V/H\,\cos \,\theta }{\frac{V}{H}}=\frac{1}{\cos \,\theta }$ Now adding 1 to both the sides. ${{\phi }_{1}}=$ $=BA$ or         ${{\phi }_{2}}=$ or $||$