Viscous drag force on a sphere in oil

Practice question

Question

A sphere of radius 0.045m moves at 0.15m/s through machine oil (η\=0.034Pa s). What is the viscous drag force?

Options

Choose one · Correct answer highlighted

0.03 N 0.04 N 0.043 N Correct 0.05 N

Explanation

Stokes’ law: F = 6πηav. η = 0.034Pa s, a = 0.045m, v = 0.15m/s. F = 6×3.14×0.034×0.045×0.15 = 0.0433N. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 0.043 N. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

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