Question

A particle of mass $m$ and charge $q$ is placed at rest in uniform electric field $E$ and then released. The kinetic energy gained by the particle after a distance $y$ is

• A. $\frac{1}{2}qEy$
• B. $qEy$
• C. $4qEy$
• D. $2qEy$

Answer 1

The correct option is B $qEy$

Initially kinetic energy $K_i$ $=0J$

After releasing of charged particle, the kinetic energy is changed. Lets say final kinetic energy is $K_f$.

Work energy theorem states that $\Delta K=W$
Therefore $K_f-K_i=F\times y$
Since $F=qE$

Then, $K_f=qEy$ (because $K_i$$=0$)