(where $g =$ acceleration due to gravity)
$(a)$ when $a =0, T =2 \pi \sqrt{\frac{\ell}{ g }}$
$(b)$ when $a =\frac{ g }{6}, T ^{\prime}=2 \pi \sqrt{\frac{\ell}{ g +\frac{ g }{6}}}$
$\therefore T ^{\prime}=\sqrt{\frac{6}{7}} T$
($A$) The amplitude of oscillation in the first case changes by a factor of $\sqrt{\frac{M}{m+M}}$, whereas in the second case it remains unchanged
($B$) The final time period of oscillation in both the cases is same
($C$) The total energy decreases in both the cases
($D$) The instantaneous speed at $x_0$ of the combined masses decreases in both the cases
