Question

A body having specific charge $8 \,\mu C / g$ is resting on a frictionless plane at a distance $10\, cm$ from the wall (as shown in the figure). It starts moving towards the wall when a uniform electric field of $100 \,V / m$ is applied horizontally towards the wall.
If the collision of the body with the wall is perfectly elastic, then the time period of the motion will be ______ $s$.

Answer 1

$F=m a$
$q E=m a$
$a=\frac{q E}{m}$
Now $d=\frac{1}{2} a t^{2}$
$t=\sqrt{\frac{2 d}{a}}$
$t=\sqrt{\frac{2 d}{\left(\frac{q E}{m}\right)}}$
$\therefore \frac{\left(\frac{8 \times 10^{-6}}{10^{-3}}\right) \times 100}{2 \times 0.1}$
$\therefore$ Time period $=2 t=1\, sec$