a
Maximum kinetic energy at lowest point $B$ is given by
$\mathrm{K}=\mathrm{mg} \ell(1-\cos \theta)$
where $\theta=$ angular amp.
$\mathrm{K}_{1}=\mathrm{mg} \ell(1-\cos \theta)$
$\mathrm{K}_{2}=\mathrm{mg}(2 \ell)(1-\cos \theta)$
$\mathrm{K}_{2}=2 \mathrm{K}_{1}$
