A source of sound is travelling towards a stationary observer. The frequency of sound heard by the observer is `25 %` more than the actual frequency. If the speed of sound is `v`, that of the source is

Options

A. 3.5 m/s
B. 3.5 cm/s
C. 3.5 ft/s
D. zero

Answer

A

Explanation

`f_1 = v/(v - v_s) f_0 , f_2 = (v)/(v + v_s) , f_0`
`f_1 - f_2 = v f_0 [1/(v - v_0) - 1/(v + v_s)]`
`f_1 - f_2 = v f_0 [(v - v_s - v + v_s)/(v^2 - v_s^2)]`
`(f_1 - f_2)/(f_0) = 2/100 = (2 v, v_s)/(v^2 - v_s^2)`
`implies v_s prop v/100 = 350/100 = 3.5 m//s`
Since speed of sound `v gt gt v_s`.