
Particle will leave the inclined plane when
$\mathrm{F}=\mathrm{mg} \cos \theta$
$\Rightarrow \mathrm{qvB}=\mathrm{mg} \cos \theta$
$v=\frac{m g \cos \theta}{q B}$
Time taken to reach $v$ is $t$
$v=g \sin \theta t$
$\mathrm{t}=\frac{\mathrm{v}}{\mathrm{g} \sin \theta}=\frac{\mathrm{mg} \cot \theta}{\mathrm{qgB}}=\frac{\mathrm{mcot} \theta}{\mathrm{qB}}$

