3. Consider a 2D flow between two parallel plates caused by moving one plate with velocity Vo

relative to the other as shown. In case I, a student calculates the force on the fixed plate using

the equation,

F = (area of plate) x μ

2

Stationary

Case I

du

dy

where u(y) is the velocity profile and w corresponds to the fixed plate. The student concludes

that for case I, as (du/dy)w is positive, the force acts to the right. The student now uses

this formula to calculate the force on the stationary plate in case II and concludes that as

(du/dy) is negative, the force on the upper plate in case II is to the left. Is the student's

analysis correct? If not, clearly indicate what the error is. Clearly show how to correct the

student's analysis, and compute the correct force on the upper plate in case II.

Stationary

Case II

(3)