Lagrangian motion (force on a plate)

[ponjavic]

I am trying to solve this problem using lagrangian motion but I have no idea how to use it.

It can be solved using mass conservation and force momentum equation but we are supposed to solve it with continuity.

How would I go about this?

Continuity:

$$\frac{ Dp }{Dt} = \delta u / \delta x + \delta v / \delta y + \delta w / \delta z$$

Now the problem is this:

Calculate the drag force acting on the flat 2m wide plate. Outside the viscous region the velocity is uniform. Use density = 1.23kg/m^3

What I can say is that, $$\frac{ \delta p }{\delta t} = 0$$

PIC

 

[ponjavic]

Nobody with a clue on this one?

The exact question states:

b) Solve the problem using a control volume with the upper boundary a streamline (no mass flux crosses a streamline)