JEE MainPhysicsMechanical Properties of Fluids
A small spherical body of mass M and density d₁ falls in a viscous liquid of density d₂ (where d₁ > d₂ ). It eventually attains a uniform terminal velocity v₀ . The rate at which heat is dissipated by the viscous drag force is:
Options
- AMg v₀
- BMg v₀ (1 + d₂ d₁ )
- CMg v₀ (1 - d₁ d₂ )
- DMg v₀ (1 - d₂ d₁ )
Correct answer
D. Mg v₀ (1 - d₂ d₁ )
Step-by-step solution
When the spherical body attains the uniform terminal velocity v₀ , the net force acting on it is zero. The forces acting on the body are its weight W downwards, the buoyant force B upwards, and the viscous drag force F_v upwards. W = B + F_v F_v = W - B The weight of the body is W = Mg . The volume of the body is V = M d₁ . The buoyant force is B = V d₂ g = ( M d₁ ) d₂ g = Mg ( d₂ d₁ ) . Substituting W and B into the equation for F_v : F_v = Mg - Mg ( d₂ d₁ ) = Mg (1 - d₂ d₁ ) The rate at which heat is dissipated b