Question

A block of mass $m$ containing a net charge of $-q$ is placed on a frictionless horizontal table and is connected to the wall through an unstretched spring of spring constant $k$ .If the horizontal electric field $E$ parallel to the spring is switched on, then the maximum compression of the spring is

• A. $\frac{2qE}{k}$
• B. $\frac{qE}{k}$
• C. zero
• D. $\sqrt{\frac{qE}{k}}$

Answer 1

The correct option is A $\frac{2qE}{k}$

Force on the block is, $F=qE$ towards left.
Let spring be compressed by a maximum distance $x$. Then, the work done on the spring is given by
$Fx=\frac{1}{2}k{x}^2\Rightarrow qEx=\frac{1}{2}k{x}^2\Rightarrow x=\frac{2qE}{k}$