Homework Help: Physics

Posted by Shawna on Monday, January 11, 2010 at 5:50pm.

The water flowing through a 1.9 cm (inside diameter) pipe flows out through three 1.3 cm pipes. (a) If the flow rates in the three smaller pipes are 24, 18, and 13 L/min, what is the flow rate in the 1.9 cm pipe? (b) What is the ratio of the speed of water in the 1.9 cm pipe to that in the pipe carrying 24 L/min?

Now I know A1v1=A2v2 and i have been converting to SI units but I am still not getting the right answer. Would it be something like A1v1=A2(v1+v2+v3)?

Physics - Damon, Monday, January 11, 2010 at 6:30pm
No water is lost or stored, just add.

call Q the flow per second in each pipe.
Q big pipe = 24+18+13 = 55 L/min
Q little pipe = 24 L/min
Vbig pipe pi rBig^2 = 55
Vsmall pipe pi rsmall^2 = 24

so Vsmall = 24/[pi(1.3^2 /4)]
vbig = 55 /[pi(1.9^2/4)]

vbig/vsmall = (55/24)(1.9^2/1.3^2)

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