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JEE Main Physics question

PhysicsWork, Energy and PowerJEE Main

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

Answer: (B)

Solution

For equilibrium, dU/dr = 0 ⟹ −2A/r³ + B/r² = 0 ⟹ r = 2A/B. (This is a stable equilibrium since d²U/dr² > 0 there.)

Question ID VK-153887