JEE Main · 2020 · 08 Jan 2020 · Shift 2 · Work, Power & Energy

A particle of mass

m

and charge

q

is released from rest in a uniform electric field. If there is no other force on the particle, the dependence of its speed v on the distance x travelled by it is correctly given by (graphs are schematic and not drawn to scale)

(A)(see structure)
(B)(see structure)
(C)(see structure)
(D)(see structure)
✓ Correct

Answer: (D)

Solution

A fixed charge in a uniform field feels a constant force, so the particle moves with constant acceleration

a = \frac{q E}{m}

from rest. Then

v^{2} = 2 a x

, giving

v = \frac{2 q E}{m} x

. Thus

v

grows as the square root of

x

, a curve rising steeply from the origin and then flattening as it bends toward the

x

-axis.

JEE Main · 2020 · 08 Jan 2020 · Shift 2 · Single correct option

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