A stationary source of sound A is producing sound of frequency $170 \mathrm{~Hz}$. Another source of sound B…
A stationary source of sound A is producing sound of frequency $170 \mathrm{~Hz}$. Another source of sound B producing sound of frequency $240 \mathrm{~Hz}$ is moving towards the source A on a straight path with a uniform speed of $20 \mathrm{~ms}^{-1}$. An observer between A and B is moving towards the source A along the straight path $\mathrm{BA}$. If the number of beats heard by the observer is zero, the speed of the observer is ____ $\mathrm{ms}^{-1}$. (Speed of sound in air $=340 \mathrm{~ms}^{-1}$).