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# Weight of copper in water

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A scale reads 380 N when a piece of copper is hanging from it. What does it read (in N) when it is lowered so that the copper is submerged in water?

I need to find out the mass of the copper right to know how much water it displaced then take the 380 minus the weight of that water?

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33 minutes ago, brickman7713 said:
A scale reads 380 N when a piece of copper is hanging from it. What does it read (in N) when it is lowered so that the copper is submerged in water?

I need to find out the mass of the copper right to know how much water it displaced then take the 380 minus the weight of that water?

Yes, you need to find the weight of water which was displaced by the object which was submerged. It will give you the buoyant force expressed in Newtons (weight is always measured in Newtons)

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Ok so how would I do that, Do I need to find the size of the object?

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21 minutes ago, brickman7713 said:

Ok so how would I do that, Do I need to find the size of the object?

Yes, calculating the volume of the piece of copper is a good start!

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Ok but how? I know the mass density is 8,930 kg/m3 and the weight density is 557 lb/ft3 and of course weight of 380 newtons.

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12 minutes ago, brickman7713 said:

Ok but how? I know the mass density is 8,930 kg/m3 and the weight density is 557 lb/ft3 and of course weight of 380 newtons﻿.﻿

Let's try this hint, in the form of a question: What mass would make the scale show 380 N?

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The figure in pounds and feet isn't likely to help in a science question.

Is there any other data given?
In particular, does it say if this experiment is on the Moon, or Earth or where?

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8 minutes ago, John Cuthber said:

The figure in pounds and feet isn't likely to help in a science question.

Is there any other data given?
In particular, does it say if this experiment is on the Moon, or Earth or where?

I assume earth so 9.8 is what I think you are referring to.

9 minutes ago, Ghideon said:

Let's try this hint, in the form of a question: What mass would make the scale show 380 N?

38.75kg ?

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21 minutes ago, brickman7713 said:

38.75k﻿g ?

Next hint: what volume of a piece of copper would have that specific mass? Could that volume help you find out how much water that is displaced?
Note; I'm assuming a solid piece of copper, not a hollow sphere or similar.

(You might want to check the rounding of the intermediate steps depending on the precision required in the final answer)

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13 minutes ago, Ghideon said:

Next hint: what volume of a piece of copper would have that specific mass? Could that volume help you find out how much water that is displaced?
Note; I'm assuming a solid piece of copper, not a hollow sphere or similar.

(You might want to check the rounding of the intermediate steps depending on the precision required in the final answer)

Is it 45.48 liters in volume then?

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8 hours ago, brickman7713 said:

Is it 45.48 liters in volume then?

That number doesn't seem quite right. Compare a volume of 45.48 liters of solid copper with the mass you calculated, what does that show? You might need to show the calculations you have done so far, that would allow for better hints about how to proceed.

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9 hours ago, Ghideon said:

That number doesn't seem quite right. Compare a volume of 45.48 liters of solid copper with the mass you calculated, what does that show? You might need to show the calculations you have done so far, that would allow for better hints about how to proceed.

Ok, that was an online tool. How does converting a mass that is solid to a liter that is liquid work?

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3 hours ago, brickman7713 said:

How does converting a mass that is solid to a liter that is liquid work?

Mass per unit volume is known as density, often denoted by letter $\rho$. Mass, density and volume is related: $\rho=\frac{m}{V}$. Since copper has $\rho=8930 kg/m^{3}$ that equals $\rho=8.930 kg/dm^{3}$. Note that $1dm^{3}=1Liter$.

So, given the mass of copper you should be able to calculate the volume of copper which equals the volume of water that is displaced. Note that Solid or liquid does not matter, the concept of volume is the same. Here is a picture of measurement of volume by displacement. The amount by which the liquid rises in the cylinder is equal to the volume of the solid rock.

Edited by Ghideon

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