Question

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 20º C , the cart is moving at 0.400 m/s, its surface area is 2.50×10−2 m 2 , and the thickness of the air layer is 6.00×10−5 m .

A) 0.00302 N

B) 0.00156 N

C) 0.0103 N

D) 0.00604 N

Answer 1

Dynamic Viscosity of air at 20º C η = 1.8205 x 10^-5 kg/m.s

velocity of cart v = 0.400 m/s

surface area of cart A = 2.50×10⁻² m ²

thickness of the air layer L =  6.00×10⁻⁵ m

retarding force due to the viscosity of the air F = (η.v.A)/L

F = (1.8205 x 10^-5 kg/m.s x 0.400 m/s x 2.50×10⁻² m ² ) / ( 6.00×10⁻⁵ m)

F = 0.00302 N