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**The potential energy of particle in a force field is U = A/r² – b/r, where A and B are positive constants and r is the distance of particle from the centre of the field. For stable equilibrium, the distance of the particle is: **

### Options

(a) B / 2A

(b) 2A / B

(c) A / B

(d) B / A

### Correct Answer:

2A / B

### Explanation:

for equilibrium dU/ dr = 0

-2A/r³ + B/r² = 0 r = 2A / B

for stable equilibrium d²U /dr² should be positive for the value of r.

here d²U / dr² = 6A/r⁴ – 2B/r³ is +ve value for r = 2A / B So.

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Topics: Electrostatics
(146)

Subject: Physics
(2479)

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