A sphere of radius 1 mm moves at terminal speed 1 cm/s through a liquid of viscosity 1 Pa·s. If the Stokes drag is Nπ × 10⁻⁵ N, find N.

Question

G1 Physics · Accepted Answer

Stokes drag is F(viscous) = 6πηrv. Substitute: η = 1 Pa·s, r = 10⁻³ m, v = 1 cm/s = 10⁻² m/s. Therefore, F(viscous) = 6π×1×10⁻³×10⁻² = 6π×10⁻⁵ N. Hence, N = 6.