a
Case-$1$ : No friction
$\mathrm{a}=\mathrm{g} \sin \theta$
$\ell=\frac{1}{2}(\mathrm{~g} \sin \theta) \mathrm{t}_1^2$
$\mathrm{t}_1=\sqrt{\frac{2 \ell}{\mathrm{g} \sin \theta}}$
Case-$2$ : With friction
$a=g \sin \theta-\mu g \cos \theta$
$\ell=\frac{1}{2}(g \sin \theta-\mu g \cos \theta) t_2^2$
$\sqrt{\frac{2 \ell}{g \sin \theta-\mu g \cos \theta}}=n \sqrt{\frac{2 \ell}{g \sin \theta}}$
$\mu=1-\frac{1}{n^2}$
