A particle of mass m and charge q is attached to a light rod of length L. The rod can rotate freely in the plane of paper about the other end, which is hinged at P. The entire assembly lies in a uniform electric field E also acting in the plane of paper as shown. The rod is released from rest when it makes an angle θ with the electric field direction. Determine the speed of the particle when the rod is parallel to the electric field.

Question

G1 Physics · Accepted Answer

Step 1: Use superposition, 𝐄 = Σ[1/(4πε₀)] qᵢ 𝐫ᵢ/rᵢ³, or the appropriate continuous-distribution integral. Step 2: Resolve components and exploit symmetry to cancel components. Step 3: Add the surviving components and compare with the choices. Final: A: 1/2 2 (1 cos ) qEL m - θ.