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 10 m/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 $10\sqrt{2}$

Body moves along the parabolic path.

For vertical motion : By using v = u + at
$\Rightarrow v_y=0+\frac{QE}{m}.t=\frac{{10}^{-6}\times {10}^3}{{10}^{-3}}\times 10=10m/sec$
For horizontal motion - It’s horizontal velocity remains the same i.e. after 10 sec, horizontal velocity of body $v_x=10m/sec$.
Velocity after 10 sec $v=\sqrt{v_x^2+v_y^2}=10\sqrt{2}m/sec$