A sphere with diameter d and density p, is released from rest and falls under the action of gravity through a fluid of density pr and viscosity μ. a) By considering a force balance upon the sphere, and assuming Stokes law for the drag force F: F= 3xud where u is the velocity of the sphere, show that the velocity of the sphere at time / is given by the equation: -(1-e) where the parameters ki and k2 are equal to: 18μ k₁ P-Pig and k₂ = d2p. P. b) A PVC sphere, 0.1 mm in diameter, with density 1350 kg m³, falls from rest through oil with 800 kg m³ density and 2x 103 Pa s viscosity. Calculate the terminal velocity of the sphere. Is the Stokes law applicable in this case?