An inclined plane making an angle of $30^{\circ}$ with the horizontal is placed in a uniform horizontal
electric field $200 \frac{\mathrm{N}}{\mathrm{C}}$ as shown in the figure. A body
of mass $1 \mathrm{~kg}$ and charge $5 \mathrm{mC}$ is allowed to slide down from rest at a height of $1 \mathrm{~m}$. If the coefficient of friction is $0.2$, find the time taken by the body
to reach the bottom. $\left[g=9.8 \mathrm{~m} / \mathrm{s}^{2}, \sin 30^{\circ}=\frac{1}{2}\right.$
$\left.\cos 30^{\circ}=\frac{\sqrt{3}}{2}\right]$
Correct Option: , 4
FBD
here $\mathrm{N}=9.8 \cos 30+1 \sin 30$ $\approx 9 \mathrm{~N}$
so $\mathrm{a}=\frac{9.8 \sin 30-1 \cos 30-\mu \mathrm{N}}{1}$
$\mathrm{a}=2.233 \mathrm{~m} / \mathrm{s}^{2}$
By $S=u t+\frac{1}{2} a t^{2}$
$=\frac{1}{2}(2.233) \mathrm{t}^{2}$
$\sin 30^{\circ}$
$\mathrm{t} \approx 1.3 \mathrm{sec}$