Question 956018
Water flows at 2 feet per second through a pipe with a diameter of 8 inches.
 A cylindrical tank with a diameter of 15 feet and a height of 6 feet collects the water.
a) What is the volume, in cubic inches, of water flowing out of the pipe every second?
The volume of water is in the shape of a cylinder 24" long (2 ft), 4 in radius ( half the diameter) 
{{{V = pi*4^2* 24}}}
V = 1206.37 cu/in/sec
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b) What is the height, in inches, of the water in the tank after 5 minutes?
Radius of the tank is 7.5 ft, change to inches 7.5(12) = 90 inches
Find how much water flows in 5 min: 1206.37 * 5 * 60 = 361911 cu/inches
let h = the height of of the water after 5 min
{{{pi*90^2*h = 361911}}}
{{{25446.9h = 361911}}}
{{{h = 361911/25446.9}}}
h = 14.22 inches
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c) How many minutes will it take to fill 75% of the tank?
Find the volume of 75% of the tank (6' = 72")
{{{pi*90^2*72*.75}}} = 1374132.63 cu/in
Find how many seconds to obtain this amt of water
{{{1374132/1206.37}}} = 1139.064 seconds
Change this to minutes
{{{1139.064/60}}} = 18.98 ~ 19 minutes to fill 3/4 of the tank
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I am ashamed to say we could have done this last question much easier.
The amt of water varies directly with the height
3/4 of the height of the tank = .75(72) = 54 inches
A simple ratio equation, let t = time for fill it 3/4 full
{{{t/5}}} = {{{54/14.22}}}
Cross multiply
14.22t = 5 * 54
14.22t = 270
t = 270/14.22
t = 18.98 the same answer we got with all that tedius calculating.
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What do you think of that?