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Hi Again!

More troubles with fluids.

I was pretty sure I had this one.

There is a

freshwater pond

density, D=1000 kg/m^3

depth = 15.1 m

one of the sides is blocked off by a cliff.

A nearly horizontal tube

diameter = 3.17 cm

depth below the pond's surface is 6.2 m

eroded to the other side of the cliff

a rock blocks cuts off the flow of the water.

The question asks for the frictional force between the tube's wall and the rock blocking the exit.

I figured it would be fairly easy, since

F = P*A

and we can find out the hydrostatic pressure.

so

P = Patm + D*g*h

P = 101300 + 1000*9.8*6.2

P = 162060 Pa

A = pi*r^2 = pi* (0.01585)^2 = 7.89e-4 m^2

and therefore,

F = P*A = 127.9 N is the force on the rock blocking the exit

because there is no acceleration, the system is at equilibrium

so Fnet = F(ontherock) - F(friction) = 0

so F(on the rock) = F(friction)

so then my answer would be 127.9 N

Could you point out where I've made an error, and push me in the right direction?

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# Fluids - bringing together pressure, depth and friction

**Physics Forums | Science Articles, Homework Help, Discussion**