1. The problem statement, all variables and given/known data Blood supply to the heart occurs through coronary arteries. Consider one of the arteries to be 2.5 mm in diameter and 3 cm in length. The average velocity of blood flow through that artery is 1.5 cm/s. Assuming the density of blood to be 1.056 g/cc and viscosity to be 3 cP (3x10-3 Ns/m2). Estimate the shear stress at the wall. 2. Relevant equations τ = μ ∂u/∂y = shear stress = (viscosity) (d(velocity))/(dy) 3. The attempt at a solution τ = (3cP)(1.5cm/s) I'm not sure how to estimate ∂u/∂y. Is it equal to the average velocity? I think that when the blood reaches fully developed flow, it's shaped like a parabola and it's velocity is constant at a given y, but I'm not sure how to apply this information to understand the formula.