# Homework Help: Fluid Mechanic

1. Sep 30, 2007

### ascll

1. The problem statement, all variables and given/known data

1)

Consider the hydraulic lift which has a smaller piston of area A1 and a larger piston area A2. Initially the two pistons are not moving.

Show that in order to raise the larger piston by a distance d2, it is necessary to apply a force △F = ρg(A1 + A2)d2 on a smaller piston

2)

The water in the lake behind a wall is 15 m deep. A horizontal pipe 4 cm in diameter passes through the wall 6 m below the water surface, which is blocked by a plug. Assume the volume of lake is so large that its surface remains constant even when water flows out of the wall.
Find the frictional force between the plug and the wall.

3. The attempt at a solution

1) for this question , i can only think about the relation of the area , force and distance , but i cannot group them up and form the equation as the question stated

F1 * d1 = F2 * d2
A1 * F2 = A2 * F1

2) i dunno where the friction come from and seems dunno what's going on in this question........

2. Sep 30, 2007

### ascll

nobody can help...........?

3. Oct 1, 2007

### learningphysics

For the first question, is there a picture given? Can you describe the picture?

For the second question... I don't understand this part: "Assume the volume of lake is so large that its surface remains constant" surface area?