JEE Main202127 Jul 2021Morning ShiftPhysicsOscillationsActual
Two identical tennis balls each having mass m and charge q are suspended from a fixed point by threads of length l . What is the equilibrium separation when each thread makes a small angle θ with the vertical?
Options
- Ax = q 2 l 2 π ε 0 m g 1 2
- Bx = q 2 l 2 π ε 0 m g 1 3
- Cx = q 2 l 2 2 π ε 0   m 2   g 1 3
- Dx = q 2 l 2 2 πε 0 m 2 g 2 1 3
Correct answer
B. x = q 2 l 2 π ε 0 m g 1 3
Step-by-step solution
T cos θ = m g T sin θ = k q 2 x 2 tan θ = k q 2 x 2 m g as tan θ ≈ sin θ ≈ x 2 L x 2 L = K q 2 x 2 m g x = q 2   L 2 π ε 0 m g 1 3