Problem 8: A cart is moving along and very close to a level air track at a speed
ID: 1781433 • Letter: P
Question
Problem 8: A cart is moving along and very close to a level air track at a speed of 0.56 m/s. The surface area of the cart's underside is 2.9 × 10-2 m2 and the thickness of the air layer between the cart and the track is 5.8 × 10-5 m. The air temperature is 20°C Part (a) Find the magnitude of the retarding force, in newtons, acting on the cart due to the viscosity of the air layer between the cart and the air track. Take the viscosity of air at the given temperature to be 1.81 × 10-5 Pa·s. Numeric A numeric value is expected and not an expression. Part (b) What is the ratio of this force to the weight of the 0.31 kg cart? Numeric : A numeric value is expected and not an expression.Explanation / Answer
a) magnitude of retarding force = n v A / L
= (1.81 * 10-5 * 0.56 * 2.9 * 10-2) / (5.8 * 10-5)
= 5.07 * 10-3 N
b) ratio F / W = 5.07 * 10-3/ 0.31 * 9.8
F / W = 1.67 * 10-3