NEET 2019 Odisha · PhysicsTerminal velocityPrevious Year Question
Two small spherical metal balls of equal mass are made from materials of densities ρ₁ and ρ₂ (ρ₁ = 8ρ₂) and have radii 1 mm and 2 mm respectively. They fall vertically from rest in a viscous medium of coefficient of viscosity η and density 0.1ρ₂. The ratio of their terminal velocities is:
Answer: (D) 79/36. v_t = (2/9)·r²(ρ_body − ρ_med)g/η, so v₁/v₂ = [r₁²(ρ₁ − ρ_m)] / [r₂²(ρ₂ − ρ_m)].
- A.79/72
- B.19/36
- C.39/72
- D.79/36✓
Correct Answer
(D) 79/36
Solution & Explanation
v_t = (2/9)·r²(ρ_body − ρ_med)g/η, so v₁/v₂ = [r₁²(ρ₁ − ρ_m)] / [r₂²(ρ₂ − ρ_m)]. = [1²(8ρ₂ − 0.1ρ₂)] / [2²(ρ₂ − 0.1ρ₂)] = (7.9)/(4 × 0.9) = 7.9/3.6 = 79/36.
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