Practice question
Question
A sphere of radius 0.015m moves at 0.2m/s through water (η\=1.0×10−3Pa s). What is the viscous force?
Explanation
Stokes’ law: F = 6πηav. η = 1.0×10−3Pa s, a = 0.015m, v = 0.2m/s. F = 6×3.14×1.0×10−3×0.015×0.2 = 5.652×10−5N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 5.65 × 10⁻⁵ N. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.