Question

A uniform electric field of 2 kNC-1 is in the x-direction. A point charge of 3 μC initially at rest at the origin is released. What is the kinetic energy of this charge at x = 4m?

Answer 1

The electric force acting on the charge is given by the charge multiplied by the electric field intensity:
$F=qE$
where in our problem $q=3 \mu C= 3 \cdot 10^{-6} C$ and $E=2 kN/C=2000 N/C$, so the force is
$F=(3 \cdot 10^{-6} C)(2000 N/C)=0.006 N$

The initial kinetic energy of the particle is zero (because it is at rest), so its final kinetic energy corresponds to the work done by the electric force for a distance of x=4 m:
$K(4 m)=W=Fd=(0.006 N)(4 m)=0.024 J$