A particle of mass m and charge q is placed at rest in a uniform electric field E and then released. The kinetic energy attained by the particle after moving a distance y is:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \( qEy \)
The work-energy theorem says that the work done by the net force equals the gain in kinetic energy. The only force on the particle is the electric force \( F = qE \), which is constant and acts along the displacement y.
\( W = Fy = qEy \)
The particle starts from rest, so its kinetic energy after moving y is
\( K = W = qEy \)
The same result follows from the potential difference: \( V = Ey \) between the two positions, and the gain in kinetic energy is \( qV = qEy \).