Question

A block of mass m having a charge q is placed on a smooth horizontal table and is connected to a wall through an unstressed spring of spring constant k as shown in figure. A horizontal electric field E parallel to the spring is switched on. Find the amplitude of the resulting SHM of the block.

Answer 1

The force due to the electric field on the mass is given as:

$F=qE$

The restoring force developed in the spring is given by:

$F=-Kx$

Where $x=$ amplitude

At maximum elongation (i.e. amplitude), the two forces will balance each other.

$qE=-Kx$

or $x=\frac{-qE}{K}$