Question

A band playing music at frequency f is moving towards a wall at a speed $v_b$. A motorist is following the band with a speed $v_m$. If v is the speed of sound, the expression for the beat frequency heard by the motorist is

• A. $\frac{v + v_m}{v + v_b} f$
• B. $\frac{v + v_m}{v - v_b} f$
• C. $\frac{2v_b (v + v_m)}{v^2 - v_b^2} f$
• D. $\frac{2v_m (v + v_b)}{v^2 - v_m^2} f$

Answer 1

Answer: (C)

$\frac{2v_b (v + v_m)}{v^2 - v_b^2} f$

Answer 2

The correct option is(C): $\frac{2v_b (v + v_m)}{v^2 - v_b^2} f$