What is the density of the wood?

In summary, to find the density of a block of wood floating in water and oil with different submerged volumes, one can draw a free-body diagram and use Newton's second law to solve for the density. Simply dividing the submerged volume by the density of the fluid will not always give the correct answer.
  • #1
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Homework Statement


A block of wood with volume V floats in water with 0.68V submerged. In oil the block floats with 0.86V of its volume submerged.

Find the density of the wood.


Homework Equations



[tex]\rho[/tex] = M/V




The Attempt at a Solution



I'm not really sure about how to attempt to solve this problem. I know the density of fresh water and that's about it. Can anyone help?
 
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  • #2
Find the density of the WOOD, not of the oil? You don't need to know about the oil for that. Just draw a free-body diagram for the block of wood and write out Newton's second law.
 
  • #3
Oh ok! I got it, thanks!
 
  • #4
Ok I got the density of the wood but I could not find the density of the oil.

For the wood this is what I did..

density of water = 1 g/cm^3
and since the volume is .68 submerged then you divide the .68 by 1g/cm^3

but this method didn't work for the oil
 
  • #5
Dividing 0.68 by 1 only worked because the density of water happened to be 1 g/cm^3, and multiplying by 1 is equivalent to dividing by it. If the density was anything else, your method would have given the wrong answer.

If you're getting confused, you should really draw a free-body diagram and write out Newton's second law instead of trying to take shortcuts. FBD + Newton's second law is a simple, elegant, and intuitive way of approaching this problem that depends only on first principles. For this problem, draw two FBD's, one for the block when it's in oil and one for the block when it's in water. Then solve the equations.
 

Related to What is the density of the wood?

1. What is the definition of density?

Density is the measure of how much mass is contained in a given volume of a substance. It is typically expressed in units of mass per unit volume, such as grams per cubic centimeter (g/cm3) or kilograms per cubic meter (kg/m3).

2. How do you find the density of wood?

To find the density of wood, you will need to know the mass and volume of the wood sample. The mass can be measured using a scale, and the volume can be calculated by measuring the length, width, and height of the wood and multiplying them together. Then, divide the mass by the volume to get the density in units of mass per unit volume.

3. What are the units for measuring the density of wood?

The density of wood is typically measured in units of mass per unit volume, such as grams per cubic centimeter (g/cm3) or kilograms per cubic meter (kg/m3).

4. Why is it important to find the density of wood?

Finding the density of wood is important because it can help determine the strength, durability, and quality of the wood. It can also be used to identify different types of wood and determine if it is suitable for a specific use or application.

5. How does the density of wood affect its properties?

The density of wood can affect its properties in several ways. A higher density wood will typically be stronger and more durable, making it suitable for construction and other heavy-duty applications. Lower density woods may be more lightweight and easier to work with, but may not be as strong or durable. The density can also affect the buoyancy of wood, with lower density woods floating on water and higher density woods sinking.

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