Question

A police in a siren car moving with a speed of 20 m per sec. And chases the theif with moving with speed if v meter per second. A police car horn the siren with 400Hz and both of them moving with the siren with 300hz .what is the velocity of the if?

Answer 1

Hey dear,


◆ Answer-
v = 330 m/s

◆ Solution-
Frequency of police car horn heard by motorcyclist is -
f1 = 400(330-v)/(330-20)
f1 = 40(330-v)/31

Frequency of the siren heard by motorcyclist is -
f2 = 300(330+v)/330
f2 = 30(330+v)/33

As no beats are observed,
f1 = f2
40(330-v)/31 = 30(330+v)/33
435600 - 1320v = 306900 + 930v
128700 = 390v
v = 330 m/s

Therefore, velocity of the thief is 330 m/s.

Hope it helps...