Question

There is a uniform electric field of strength ${10}^{3}V/m$ along $y-axis$. A body of mass $1g$ and charge ${10}^{-6}C$ is projected into the field from origin along the positive $x-axis$ with a velocity $10m/s$. Its speed in m/s after $10s$ is (neglect gravitation) :

• A. $10$
• B. $5\sqrt{2}$
• C. $10\sqrt{2}$
• D. $20$

Answer 1

The correct option is C $10\sqrt{2}$

Velocity in $x$ direction remains constant i.e, $v_x=10m/s$
Now acceleration is only in y direction
$a=\frac{qE}{m}$

$a=\frac{{10}^3\times {10}^{-6}}{1\times {10}^{-3}}$

$\therefore$ Velocity in y direction $v_y=a\times t$
$v_y=10m/s$
$\therefore v=10\hat{x}+10\hat{y}$

$\left|v\right|=10\sqrt{2}$