Question

1. The siren of a police car emits a sound with a frequency of 70 Hz. The police (P) is chasing a criminal (C) as shown in the figure below. The police car moves at 30 m/s, whereas the criminals car is moving at 10 m/s. What is the frequency of the sound emitted by the siren as heard by the criminal?​

Answer 1

Explanation:

Correct option is D)

Case (i),

f

1

=f

0

(

Vs−U

s

Vs−U

0

)

=f

0

(

330−30

330−U

)=180

300

(330−U)

f

1

=180(

330

330−U

)...(i)

Case (ii), f

2

=160(

330

330+U

)...(ii)

∵ There is no beats

∴f

1

=f

2

180(

300

330−U

)=160(

330

330+U

)

⇒9(

300

330−U

)=160(

330

330+U

)

⇒

10

9

(330−U)=

11

8

(330+U)

⇒32670−99U=26400+80U

∴U=

179

6270

=35.02m/s