Question

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

• A. $qEy$
• B. $qEy^2$
• C. $q^2Ey$
• D. $qE^2y$

Answer 1

Answer: (A)

$qEy$

Answer 2

Velocity gained after moving a distance y is $v^{2}=u^{2}+2 ay$
$Here\, u=0\, and\, a=\frac{qE}{m}$
$v^{2}=2\left(\frac{qE}{m}\right)y$
$Kinetic \,energy, E=\frac{1}{2} mv^{2}$
$=\frac{1}{2}\times m\times\left(2\times\frac{qE}{m}\times y\right)$
$E=q\,Ey$