Viscosity and Laminar Flow; Poiseuille’s Law (Problem 29)

(a) Calculate the retarding force due to the viscosity of the air layer between a cart and a level air track given the following information—air temperature is $\text{20º C}$, the cart is moving at 0.400 m/s, its surface area is $2.50\times {10}^{-2}{\text{m}}^2$, and the thickness of the air layer is $6.00\times {10}^{-5}\text{m}$. (b) What is the ratio of this force to the weight of the 0.300-kg cart? Select the answer to part (a).