
$\mathrm{v}=\sqrt{\frac{\mathrm{T}}{\mu}}=\sqrt{\frac{\mu_{0} \mathrm{x}^{2} \mathrm{g}}{2. \mu_{0} \mathrm{x}}}$
$v=\sqrt{\frac{x g}{2}}$
$a=\frac{v d v}{d x}=\sqrt{\frac{x g}{2}} \sqrt{\frac{g}{2}} \cdot \frac{1}{2 \sqrt{x}}=\frac{g}{4} \,m / s^{2}$
${l_0} = \frac{1}{2} \times \frac{{\rm{g}}}{4}{{\rm{t}}^2} \Rightarrow {\rm{t}} = \sqrt {\frac{{8{l_0}}}{{\rm{g}}}} $
($A$) $v_P+v_R=2 v_Q$
($B$) 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)
