Question

A block of mass m and charge q is tied to a spring of spring constant k. The electric field intensity E is switched ON. the maximum displacement in the spring is

• A. $\frac{Eq}{2k}$
• B. $\frac{Eq}{m}$
• C. $\frac{2Eq}{k}$
• D. $\frac{Eq}{2m}$

Answer 1

The correct option is C $\frac{2Eq}{k}$

Max displacement occurs when all the work done by F(Eq) is stored as potential energy of spring i.e when K.E (kinetic energy) of block is $0$

$\therefore$ Work done by force in moving block by $W_x=Eqx$

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

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

$\therefore Maxdisplacement=\frac{2Eq}{k}$