Two Questions on Archimedes's Principle

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In summary: Let's look at your problems one at a time. It is better not to post multiple problems in one thread becaue it can lead to confusion as people respond to one problem or another.
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Homework Statement


A block of wood weighs 50.0 N when weighed in air. A sinker is attached to the block, and the weight of the wood-sinker combination is 200 N when the sinker alone is immersed in water. Finally, the wood-sinker combination is completely immersed and the weight is 140 N. What is the density of the block?



Homework Equations


(I'm not so sure how to write out equations on here, being my first post, so bear with me...)

B=(rho)*V*g
SumF_y=0
(rho)=m/V
And that's really all I can come up with...


The Attempt at a Solution


I haven't been able to get a good start on this problem, but I think it will have to do with the buoyancy force-weight of the system=0. I'm really not sure on this one...


And the second question... I probably shouldn't expect anyone to waste this much time helping me, lol...

Homework Statement


A solid copper ball with a diameter of 3.00 m at sea level is placed at the bottom of the ocean, at a depth of 10.0 km. If the density of the seawater is 1030 kg/m^3, how much does the diameter of the ball decrease when it reaches bottom?


Homework Equations


(rho)=m/V
V_sphere=[4(pi)r^3]/3
P=P_o+(rho)gh


The Attempt at a Solution


P=1.01x10^5+(1030)(9.8)(1.0x10^4)

My problem is, how do I relate the pressure, P, to the density and volume of the ball?



I guess the majority of my problems are conceptual. I sometimes don't understand how to begin a problem, or which equations to use in order to find my variables. Does anyone have any good general tips for my situation? Thanks for looking, and I hope this isn't too much for someone to help me out with...
 
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  • #2
Let's look at your problems one at a time. It is better not to post multiple problems in one thread becaue it can lead to confusion as people respond to one problem or another.

For number one, use the information given in the problem to determine the buoyant force on the block when it is submerged. Once you know that you can find its volume, and since you know its true weight, you can find its density.
 
  • #3
Did you ever solve this? I have the exact same question and need some help.

any ideas? I came up with a density for the block of wood of 5000 g/cm^3

feel free to reply to <email address deleted>

.excel said:

Homework Statement


A block of wood weighs 50.0 N when weighed in air. A sinker is attached to the block, and the weight of the wood-sinker combination is 200 N when the sinker alone is immersed in water. Finally, the wood-sinker combination is completely immersed and the weight is 140 N. What is the density of the block?



Homework Equations


(I'm not so sure how to write out equations on here, being my first post, so bear with me...)

B=(rho)*V*g
SumF_y=0
(rho)=m/V
And that's really all I can come up with...


The Attempt at a Solution


I haven't been able to get a good start on this problem, but I think it will have to do with the buoyancy force-weight of the system=0. I'm really not sure on this one...


And the second question... I probably shouldn't expect anyone to waste this much time helping me, lol...

Homework Statement


A solid copper ball with a diameter of 3.00 m at sea level is placed at the bottom of the ocean, at a depth of 10.0 km. If the density of the seawater is 1030 kg/m^3, how much does the diameter of the ball decrease when it reaches bottom?


Homework Equations


(rho)=m/V
V_sphere=[4(pi)r^3]/3
P=P_o+(rho)gh


The Attempt at a Solution


P=1.01x10^5+(1030)(9.8)(1.0x10^4)

My problem is, how do I relate the pressure, P, to the density and volume of the ball?



I guess the majority of my problems are conceptual. I sometimes don't understand how to begin a problem, or which equations to use in order to find my variables. Does anyone have any good general tips for my situation? Thanks for looking, and I hope this isn't too much for someone to help me out with...
 
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FAQ: Two Questions on Archimedes's Principle

1) What is Archimedes's Principle?

Archimedes's Principle is a scientific law that states that the buoyant force on an object submerged in a fluid is equal to the weight of the displaced fluid. In simpler terms, it explains why objects float or sink in water.

2) Who is Archimedes and why is this principle named after him?

Archimedes was a Greek mathematician, physicist, engineer, inventor, and astronomer who lived in the 3rd century BC. He discovered this principle while trying to determine if a crown was made of pure gold or not. It is named after him because he was the first to accurately describe and prove this principle.

3) How does Archimedes's Principle apply to real-world situations?

This principle has many practical applications, such as in shipbuilding, where it helps determine the design and stability of a ship. It is also used in determining the purity of substances and in designing flotation devices such as life jackets and boats.

4) Is Archimedes's Principle always true?

Yes, Archimedes's Principle is a fundamental law of physics and is always true. However, it may not hold in certain extreme conditions, such as in very high or low gravity environments.

5) What is the formula for calculating the buoyant force using Archimedes's Principle?

The formula for calculating the buoyant force is FB = ρVg, where ρ is the density of the fluid, V is the volume of the displaced fluid, and g is the gravitational acceleration. This formula is based on Archimedes's Principle and can be used to determine the buoyant force on an object submerged in a fluid.

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