A 256 Hz source moves toward a wall at 5 m s⁻¹. How many beats per second are heard due to direct and reflected sound? Take sound speed = 330 m s⁻¹.
Physics · Wave Motion
JEE Mains Practice

Question

A 256 Hz source moves toward a wall at 5 m s⁻¹. How many beats per second are heard due to direct and reflected sound? Take sound speed = 330 m s⁻¹.

G1 Physics · Accepted Answer

Step 1: The wall receives f₁=fv/(v−u). The reflected wave returns and is heard by the moving source/observer, giving f₂=f(v+u)/(v−u). Step 2: Beat frequency = f₂−f = f[2u/(v−u)]. With f=256, u=5, v=330, this is ≈7.9 Hz ≈ 8 Hz.