Find Specific Gravity of 8.3 kg Block in Water

In summary, to find the specific gravity of a block submerged in water, you need to find the weight of the block in air and in water, and use the formula SG = weight in air / (weight in air - weight in water). Then, to find the density of the block, you need to find the mass of the displaced water and use the formula density = mass/volume. Finally, the specific gravity is found by dividing the density of the block by the density of water (1000 kg/m^3).
  • #1
jti3066
46
0

Homework Statement



A 8.3 kg block of some unknown material is suspended from a spring scale and submerged in water. The spring scale reads 46.9 N. What is the specific gravity of the block?




Homework Equations



SG = density of object/density of reference material (water = 1000 kg/m^3)

density = mass/volume

The Attempt at a Solution



How do I find the density of the object if I do not know its volume?
 
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  • #2
Find the weight of the block mg in air.
Weight in water is given. Find loss of weight. That is equal to weight of the displaced liquid. From that you can find the volume of the block.
 
  • #3
so...

weight in air = 8.3 * 9.81 = 81.42 N

differnce = 81.42 - 46.9 = 35.523 N (weight of displaced liquid)

Density = m/v so

1000 = 35.523/v ...v = .035523 (volume of block)

density of block = m/v = 8.3/.035523 = 233.65

SG ( of block) = 233.65/1000 = .233

I did this and I get the wrong answer
 
  • #4
35.523 N is the weight of the displaced water. Find the mass of the displaced water. And then find the density of the block.
 
  • #5
ok...

mass of displaced water is 3.21 kg

1000 = 3.21/v...v= 0.00321

Density of block = 8.3/0.00321 = 2585.669

SG = 2585.669/1000 = 2.585

Still getting wrong answer
 
  • #6
can someone just show me the step by step solution please...That way I can know exactly know what I am doing wrong instead of doing the wrong steps over and over...TIA
 
  • #7
35.523n/9.8 =---?
 
  • #8
SG = 81.42/(81.42 - 46.9) = 2.36

Thanks for your help though
 
  • #9
Now for the density of block...

D = 8.3/.0035 = 2.37 * 10^3 kg/m^3
 

1. What is specific gravity?

Specific gravity is a measure of how dense a substance is compared to the density of water. It is typically represented as a ratio or decimal and has no units.

2. How do you find the specific gravity of a block in water?

To find the specific gravity of a block in water, you will need to measure the weight of the block in air and in water. Then, you can calculate the specific gravity by dividing the weight in air by the weight in water.

3. Why is it important to know the specific gravity of a block in water?

Knowing the specific gravity of a block in water can help determine the density and composition of the block. This information can be useful in various industries such as construction, metallurgy, and engineering.

4. Can the specific gravity of a block in water change?

The specific gravity of a block in water will remain constant as long as the temperature and pressure of the water do not change. However, if these factors do change, the specific gravity may also change.

5. How does the specific gravity of a block in water relate to its buoyancy?

The specific gravity of a block in water is directly related to its buoyancy. If the specific gravity is less than 1, the block will float in water. If the specific gravity is equal to or greater than 1, the block will sink in water.

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