Two spheres of equal radius fall through the same viscous liquid and both obey Stokes' law. Their densities are ρ₁ and ρ₂, while the liquid density is ρ. If their terminal speeds are v₁ and v₂, what is v₁/v₂?
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Question

Two spheres of equal radius fall through the same viscous liquid and both obey Stokes' law. Their densities are ρ₁ and ρ₂, while the liquid density is ρ. If their terminal speeds are v₁ and v₂, what is v₁/v₂?

Options

G1 Physics · Accepted Answer

For a sphere falling under Stokes' law, vₜ = 2r²(ρₛ−ρₗ)g/(9η). For the two spheres, r, η, g and liquid density ρ are the same. Therefore, v₁/v₂ = (ρ₁−ρ)/(ρ₂−ρ). Correct option: B.