Question

A person feels 2.5% difference of frequency of a motor-car horn. If the motor-car is moving to the person and the velocity of sound is 320 m/sec, then the velocity of car will be

• A. 8 m/s (approx.)
• B. 5 m/s
• C. 7 m/s
• D. 6 m/s (approx.)

Answer 1

The correct option is A

8 m/s (approx.)

By Ddoppler's formula $n^{\prime }=\frac{nv}{(v-v_s)}$

Since, source is moving towards the listener so

n' > n .

If n = 100 then n' = 102.5

$\Rightarrow 102.5=\frac{100\times 320}{(320-v_s)}\Rightarrow v_S=8m/sec$