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A particle having mass m and charge q is at rest. On applying a uniform electric field E on it, it starts moving. What is its kinetic energy when it has travelled a distance x in the direction of the force?

Asked in GUJCET 2014 · Deflection and projectile motion

Answer: (4) qEx

Step-by-step solution

Given: charge q, mass m, starting from rest in a uniform field E; it moves a distance x along the force.

Idea: work-energy theorem: the work done by the electric force equals the gain in kinetic energy.

Force F = qE, constant and along the motion.

Work W = Fx = qEx

K = 0 + W = qEx. The mass decides how quickly this energy is gained, not how much is gained per metre.

So the kinetic energy is qEx.

Why the other options are wrong

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