A vehicle sounding a whistle of frequency 256 Hz is moving on a straight road, towards a hill with a velocity of $10\;ms^{-1}$. The number of beats per second observed by a person travelling in the vehicle is : (Velocity of sound=330 \;ms^{-1})

Question

\[\begin {array} {1 1} (a)\;zero & \quad (b)\;10 \\ (c)\;14 & \quad (d)\;16 \end {array}\]