Question

A charged particle of mass $m$ and charge $q$ is released from rest in an electric field of constant magnitude $E$. The kinetic energy of the particle after time $t$ is

• A. $\frac{2 E^{2} t^{2}}{m q}$
• B. $\frac{E^{2} q^{2} t^{2}}{2 m}$
• C. $\frac{E q^{2} m}{2 t^{2}}$
• D. $\frac{E q m}{2 t}$

Answer 1

Answer: (B)

$F=q E$
$a=\frac{F}{m}=\frac{q E}{m}$
$v=a t=\frac{q E t}{m}$
Kinetic energy $=\frac{1}{2} m\left[\frac{q E t}{m}\right]^{2}=\frac{E^{2} q^{2} t^{2}}{2 m}$