Question

When an engine passes near to a stationary observer then its apparent frequencies occurs in the ratio 5/3. If the velocity of engine is ______.

Options

• 540 m/s

• 270 m/s

• 85 m/s

• 52.5 m/s

Answer 1

When an engine passes near to a stationary observer then its apparent frequencies occurs in the ratio 5/3. If the velocity of engine is 85 m/s.

Explanation:

When engine coming to the observer, then

frequency (f₁) = `f[v/(v - v_s)]`

When engine going away from the observer

`(f_2) = f[v/((v + v_s))]`

`f_1/f_2 = ((v -  v_s))/((v + v_s)`

`5/3 = (v -  v_s)/(v + v_s)  ⇒ 2v = 8v_s`

⇒ `v_s = 2/8v = 2/8 xx 340 = 85` m/s