# How many lbs. of water are in the tank?

• jim1174
In summary, a tank with a volume of 8000 gallons and 50% full will contain 4000 gallons of water. With a density of 8.33 lbs/gallon, the mass of water in the tank is 33320 lbs.

## Homework Statement

2. A tank has a volume of 8000 gallons and is 50% full. If the tank contains water, which has a density of 8.33 lbs/gallon, how many lbs. of water are in the tank?

## The Attempt at a Solution

Volume occupied is 50% i.e 4000 gallons , given that the density is 8.33 lbs/gallons

Therefore, the mass occupied by water in lbs is given by
mass =volume x density = 8000gallon x 8.33/gallon33320

https://www.physicsforums.com/file:///C:/Users/Jim/AppData/Local/Temp/msohtmlclip1/01/clip_image002.gif [Broken]

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jim1174 said:

## Homework Statement

2. A tank has a volume of 8000 gallons and is 50% full. If the tank contains water, which has a density of 8.33 lbs/gallon, how many lbs. of water are in the tank?

## The Attempt at a Solution

Volume occupied is 50% i.e 4000 gallons , given that the density is 8.33 lbs/gallons

Therefore, the mass occupied by water in lbs is given by
mass =volume x density = 8000gallon x 8.33/gallon33320

https://www.physicsforums.com/file:///C:/Users/Jim/AppData/Local/Temp/msohtmlclip1/01/clip_image002.gif [Broken]
What's your answer? The last thing you wrote was "8000gallon x 8.33/gallon33320", which makes no sense.

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jim1174 said:

## Homework Statement

2. A tank has a volume of 8000 gallons and is 50% full. If the tank contains water, which has a density of 8.33 lbs/gallon, how many lbs. of water are in the tank?

## The Attempt at a Solution

Volume occupied is 50% i.e 4000 gallons , given that the density is 8.33 lbs/gallons

Therefore, the mass occupied by water in lbs is given by
mass =volume x density = 8000gallon x 8.33/gallon33320

https://www.physicsforums.com/file:///C:/Users/Jim/AppData/Local/Temp/msohtmlclip1/01/clip_image002.gif [Broken]
well, in the US system of measure , lb or lbs is a force or weight unit, not a mass unit. Density is weight per unit volume. Weight is density x volume.

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In standard usage in the U.S. the term "pound" can denote either a unit of force or of mass. It is most commonly used in the sense of a mass. But that is irrelevant here. The problem states as a given that water has a density of 8.33 pounds per gallon. So for purposes of the problem we may safely assume that water has a density of 8.33 pounds per gallon. Whether that "8.33 pounds" is intended to denote the gravitational downforce on a gallon of water or is intended to denote the mass of a gallon of water will not change the numerical value of the intended answer to the problem and will not change the name of the unit of measure in which that result should be reported.

But we digress. Mark44's request for clarification is appropriate.

PhanthomJay said:
well, in the US system of measure , lb or lbs is a force or weight unit, not a mass unit. Density is weight per unit volume. Weight is density x volume.
As another guy who grew up with the US system, I can tell you that the clear implication is lbm (as indicated by jbriggs444).

Regarding the OPs calculation, he calculated 4000 gallons, but then still used 8000 gal in the mass calculation. Go figure.

Chet

Oh here we go again. A lb is a force unit, sometimes denoted lbf by those unfamiliar with US units. A pound of mass, which is used by virtually no one, is designated lbm. A gallon of water weighs 8.33 pounds in the US. No one cares that it has a mass of 8.33 lbm, not in the layman's world nor in the technical world. When mass must be used technically, we take its Earth weight in lbs and divide by 32 and don't give it a name, even though that mass unit is slugs.

is this the answer mass= volume*density= 4000gallon*8.33lb/gallon=3332

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jim1174 said:
is this the answer mass= volume*density= 4000gallon*8.33lb/gallon=3332
No, it's not.

And the units of the answer would be lb.

jim1174 said:
is this the answer mass= volume*density= 4000gallon*8.33lb/gallon=3332

Always double check your arithmetic, and make sure you copy down results correctly. You multiplied 4000 by 8.33 and wound up with a number which was less than 4000.

Volume occupied is 50% i.e. 4000 gallons, given that the density is 8.33 lbs/gallons

Therefore, the mass occupied by water in lbs is given by
mass =volume x density = 4000gallon x 8.33lbs/gallon=33320 lbs

Final Answer is = 33320 lbs

## 1. How do you calculate the weight of water in a tank?

The weight of water in a tank can be calculated by multiplying the volume of the water in the tank (in cubic feet) by the density of water (62.4 pounds per cubic foot).

## 2. How do you measure the volume of water in a tank?

The volume of water in a tank can be measured by multiplying the length, width, and height of the tank (in feet) together. This will give you the volume of the tank in cubic feet.

## 3. How do you determine the density of water?

The density of water is a well-known value of 62.4 pounds per cubic foot. This value is based on the weight of one cubic foot of water at 39.2°F (4°C).

## 4. Can you use a different unit of measurement for the weight of water in a tank?

Yes, you can use different units of measurement for the weight of water in a tank, such as kilograms or tons. To convert the weight of water from pounds to another unit, you would need to know the conversion factor for that specific unit.

## 5. How do factors such as temperature and pressure affect the weight of water in a tank?

Temperature and pressure can affect the weight of water in a tank. As temperature increases, the volume of water will expand and therefore, its weight will also increase. Pressure can also affect the weight of water, as a higher pressure will result in a higher density and therefore, a higher weight. It is important to take these factors into consideration when calculating the weight of water in a tank.