Question

I can't solve the problem(b)
I guess I have to use the fact that the pressure varies with depth, but I can't apply that properly.

Answer 1

Hi

You are saying that you have done part a. So I am skipping it.

For part b, you just have to show the components of the force with which one of the ends of the boom is pulling the dock. The boom will pust because the layer of oil will put pressure on the boom and therefore in turn the boom will put pressure on the dock as the ends of the boom is attached to the dock.

There will be no parallel force on the dock because the boom will pull the dock in perpendicular direction only

As Pressure =Force/Area

So: Force = Pressure * Area

F = row*g*h*Area (direction will be perpendicular to the dock)

Thats your answer!!:D