A person observes a change of 2.5 % in frequency of sound of horn of a car. If the car is approaching forward the person & sound velocity is 320 m/s, then velocity of car in m/s will be approximaterly :-

Options

A. 8
B. 800
C. 7
D. 6

Answer

A

Explanation

`Deltaf=f_(app)-f_(o)=f_(o)((v)/(v-_(s)))-f_(o)`
`(Deltaf)/(f_(o))=(v)/(v-v_(s))-1=(v_(s))/(v-v_(s))=(2.5)/(100)`
`rArr (v_(s))/(v-v_(s))=(1)/(40)rArrv_(s)=(v)/(41)=8m//s`