# Homework Help: Find the torque on a bent pipe

1. Sep 23, 2012

### thshen34

1. The problem statement, all variables and given/known data
Consider a steady flow of liquid with a density of 805 kg/m3 through a rotating tube as shown in the sketch. The flow speed is V = 5 m/s. If ω = 10 rad/s, find the torque necessary to rotate the pipe. Assume a uniform velocity distribution at the exit from the pipe, and that the
incoming fluid has no angular momentum.

2. Relevant equations

Conversation of momentum and Rotational Forces

3. The attempt at a solution
So I calculated the force of the fluid on the pipe, which is ρV(∏D^4)/4, which can be split up to y and x components, by multiplying cosθ and sinθ, respectively. However, this does not create any moment about the axis of rotation. So, my guess is that the x component of the force provides the centripetal force of the ω rotation. Given that F = mv^2/r, I'm thinking that the we can find the torque by Fr = mv^2, since we know v. Now, can someone help me find out what m ought to be? Is it just the mass of the bent pipe portion?

I think this is a valid attempt a solution, I only need a bit of concept cleared up. I hope someone will review this question please.

Thanks,

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Last edited: Sep 23, 2012