Two identical tuning forks vibrating at the same frequency 256 Hz are kept fixed at some distance apart. A listener runs between the forks at a speed of 3.0 m/s so that he approaches one tuning fork while receding from the other (figure). Find the beat frequency observed by the listener. Speed of sound in air = 332 m/s.
Here given velocity of the sources vs = 0
Velocity of the observer v0 = 3 m/s
So, the apparent frequency heard by the man from the tuning fork in front= f′=(332+3332)×256= 258.3
the apparent frequency heard by the man from the tuning fork behind him=f”=[(332−3)332]×256=253.7Hz.
So, beat produced by them = 258.3 - 253.7 = 4.6 Hz