Question

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

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

Answer 1

Answer: (B)

2qE/k

At the point of max compression

$\text{Work done by spring = Potential due to the charge}$

$W_{spring}=V_q$

$\frac{1}{2}k{x}^2=Eqx$

$x=\frac{2Eq}{k}$