The velocity of the wave is $.....ms ^{-1}$ [all the quantities are in SI unit]
$(A)$ The number of nodes is $5$ .
$(B)$ The length of the string is $0.25 \ m$.
$(C)$ The maximum displacement of the midpoint of the string its equilibrium position is $0.01 \ m$.
$(D)$ The fundamental frequency is $100 \ Hz$.
($A$) $v_P+v_R=2 v_Q$
($B$) The rate of change in beat frequency is maximum when the car passes through $Q$
($C$) The plot below represents schematically the variation of beat frequency with time
(image)
($D$) The plot below represents schematically the variation of beat frequency with time
(image)