Practice question
Question
A sphere of radius 0.05m moves at 0.11m/s through blood (η\=2.7×10−3Pa s). What is the viscous drag force?
Explanation
Stokes’ law: F = 6πηav. η = 2.7×10−3Pa s, a = 0.05m, v = 0.11m/s. F = 6×3.14×2.7×10−3×0.05×0.11 = 0.0028N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 0.0028 N. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.