Question

Water flows out of a big tank along a horizontal tube AB of length l and radius r and bent at right angles at the other end as shown in the figure. The rate of flowis Q m³ /s. Calculate the moment of the force exerted by the water on the tube about the end A.

Answer 1

Q = AV

But A = πr^2

So, V = Q/πr^2

Force = pAV^2 , p = density of water

Force = p(AV)V

We know AV = Q and V = Q/πr^2

So, Force = p x Q x Q/πr^2

Since , length is not negligible here,
Force = pQ^2l/ πr^2