Question

A car is moving with a constant velocity 10 m/s towards a stationary wall. An observer in between the car and the wall is moving with a constant velocity 2 m/s towards the stationary wall. The car blows a horn of frequency 320 hz. The velocity of sound in air is 330 m/s. The beats frequency received by the observer is ....... Hz

Answer 1

Answer:

Frequency heard by wall

where car is source and wall is object

f

wall

=f

d1

V

S

−V

C

V

S

(i)

now the reflected sound heard by driver

in this case wall is source and car is object

f

d2

=f

wall

V

S

V

S

+V

C

(ii)

Using equation (i) and(ii)

f

d2

=f

d1

V

S

−V

C

V

S

+V

C

f

d2

=400

340−10

340+10

=400×

330

350

=424Hz