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Find the height of each right cylinder

  • #1

Homework Statement


I have to construct 8 concrete right cylinders for hurricane protection on windows, but I need to know the height to fit the given criteria. Each has a 4 inch radius and each weighs 1200 pounds. Concrete weighs 150 pounds per cubic foot.

V= volume of right cylinder
r=radius
h= height of right cylinder

Homework Equations


V=pi*r^2*h

The Attempt at a Solution


V=pi*r^2*h
1200 lbs= pi*16*h
h=23.8732 inches (1’11.87”).

I just don’t know where the weight of concrete, 150 pounds per cubic foot, comes into play. Thank you very much.
 

Answers and Replies

  • #2
Charles Link
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:welcome:You need to work in feet, not inches, and the equation you are missing is ## W=\delta \, V ##, where ## \delta ## is the density in pounds per cubic foot. When you compute the volume, the radius ## r ## needs to be converted to "x" feet. The answer you get for height ## h ## will be in feet.
 
  • #3
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In your statement, you set V=1200 pounds. That is not right; ##V=\frac{weight}{density}##. The density is what give is 150 pounds per cubic foot.
 
  • #4
:welcome:You need to work in feet, not inches, and the equation you are missing is ## W=\delta \, V ##, where ## \delta ## is the density in pounds per cubic foot. When you compute the volume, the radius ## r ## needs to be converted to "x" feet. The answer you get for height ## h ## will be in feet.
Would I be correct if I said it would have to be 22.96 feet?
 
  • #5
Ray Vickson
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Homework Statement


I have to construct 8 concrete right cylinders for hurricane protection on windows, but I need to know the height to fit the given criteria. Each has a 4 inch radius and each weighs 1200 pounds. Concrete weighs 150 pounds per cubic foot.

V= volume of right cylinder
r=radius
h= height of right cylinder

Homework Equations


V=pi*r^2*h

The Attempt at a Solution


V=pi*r^2*h
1200 lbs= pi*16*h
h=23.8732 inches (1’11.87”).

I just don’t know where the weight of concrete, 150 pounds per cubic foot, comes into play. Thank you very much.
If the final object weighs 1200 lb and concrete weighs 150 lb/cu.ft., how many cubic feet of concrete does the object consist of? So, what is the object's volume, in cubic feet?
 
Last edited:
  • #6
symbolipoint
Homework Helper
Education Advisor
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You have the volume formula, and you know how much concrete and you have the density. So?

Convert 1200 pounds into the quantity in cubic feet.
Now use your volume formula to calculate the unknown height.
 

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