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A particle having mass m and charge q is initially at rest in a constant electric field E. If it is allowed to move freely, what will be its kinetic energy after it has travelled a distance x?

1. qE²
2. qE x
3. qE y
4. qE y

Correct answer: qE x

Solution

Constant force qE acts over distance x, so KE gained = work done = qE*x.

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