A car sounding its horn at 480 Hz moves towards a high wall at a speed of `20 ms^-1`. If the speed of sound is `340 ms^-1`, the frequency of the reflected sound heard by the passenger sitting in the car will be nearest to

Options

A. 480 Hz
B. 540 Hz
C. 510 Hz
D. 570 Hz

Answer

B

Explanation

The apparent frequency striking the wall is
`v. = ((V)/(V - U_(s))) . V = (340xx480)/(340 - 20) = 510 ` Hz
After reflection the wall acts as source and man sitting in the car as observer who is moving towards the wall.
`therefore v.. = ((V + U_(0))/(V) ) . v. = ((340 + 20)/(340) ) 510 = 540 `Hz.
thus correct choice is (b).