How Many Gallons In A .75 Inch Diameter Cylinder 47 Feet Long?


2 Answers

Vincent Davis Profile
Vincent Davis answered
In order to solve this problem you will need to know the area of the circle 0.75_in in diameter which is calculated as follows: 0.75_in X pi (pi=3.1416) which is approximately equal to 2.3_in2 then multiply this answer by the no. Of inches in 47_ft: To convert 47_ft to inches multiply 47_ft by 12_in/1_ft=547_inches to calculate the ttl volume in inches multiply 547_in x 2.3_in2=1258_in3 now we convert 1258_in3 to gallons which is as

follows, in this case I will not provide the conversion factor for converting from 1_in3 to gallons I will provide only the answer which is approx. 5.4_gallons.
Oddman Profile
Oddman answered
The volume of the pipe is given by
v = (Pi/4)d2*L
  = (Pi/4)(.75 in)2(47 ft)(12 in/ft)
  ≈ 249.168 in3 = (249.168 in3)(1 gal/(231 in3)) ≈ 1.08 gal
thanked the writer.
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Oddman commented
The answer 156 gal doesn't pass a sanity check. If the volume were really that large, it would take the better part of an hour for the hot water to get to your tap from the water heater.
dan cooper
dan cooper commented
Your right, I missed a step. We are both wrong but me more than you, I'll do it right this time .75 divided by 12=.063 then (.785)(.063)(.063)(47)(7.48)=1.095
Oddman commented
If you want the answer accurate to 4 significant figures, you need to carry at least that many in all of the constituent numbers. By rounding (3/4)/12 = 1/16 to 2 digits (0.063), you automatically introduce an error of +0.8%, one that is multiplied to 1.6% when you square the number. When you subtract 1.6% from 1.095, it comes awfully close to my 1.08. The exact answer is (423/1232)π gal. To calculator accuracy, that is 1.078647477652989 gal. Pipe dimensions are 2 digits; so 3 is good enough.

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