Calculating upthrust on a solid object

  • Thread starter Thread starter azsx11
  • Start date Start date
  • Tags Tags
    Solid Upthrust
AI Thread Summary
The discussion focuses on calculating the upthrust acting on an object submerged in two different liquids. The object has a volume of 30 m³ and floats in a liquid with a density of 30 g/cm³, displacing 45,000 kg of liquid, resulting in an upthrust of 450,000 N. When placed in a second liquid with a density of 1 g/cm³, the calculations suggest that the upthrust would be 15,000 N. Participants express confusion about the calculations and the principles of buoyancy, particularly regarding whether the object sinks or floats in the second liquid. The conversation emphasizes the need to clarify the relationship between the weight of the object and the weight of the displaced liquid to determine the correct upthrust value.
azsx11
Messages
4
Reaction score
0
Calculating upthrust on an object

Homework Statement



An object made entirely of one material has a volume of 30m3. It floats in a liquid of density 30 g/cm3 with only half it's mass below the liquids surface. The object is then placed in a liquid of the same volume but with a density of 1 g/cm3. If the final upthrust that will act on the object is expressed in the form a*10bN give the values of a and b. Assume g to be 10 ms2

Homework Equations



d=m/v

The Attempt at a Solution



1st liquid

3000=m/30
=90000
90000/2 = 45000 Kg displaced

45000 * 10 = 450000 N upthrust (archimedes)
45000/3 = 15000 N upthrust in 2nd liquid

a=1.5, b=4

I honestly have no idea really.
 
Last edited:
Physics news on Phys.org
Hi azsx11, welcome to pF.
How did you get
3000 = m/30?
 
rl.bhat said:
Hi azsx11, welcome to pF.
How did you get
3000 = m/30?

Sorry, I got my order wrong.

d = 30 g/cm3 = 30000 Kg/m3

30000 = m/30

m= 900000 Kg

etc...

Is this the right way to approach the question?
 
When the body is floating, weight of the body is equal to the weight of the displaced liquid.
So what is the weight of the object?
In the second liquid whether the object sinks or floats?
If it sinks, what is the weight of the displaced liquid?
 
rl.bhat said:
When the body is floating, weight of the body is equal to the weight of the displaced liquid.
So what is the weight of the object?
In the second liquid whether the object sinks or floats?
If it sinks, what is the weight of the displaced liquid?

This is what I've tried to do.

900000/2 - half of the object is submerged.

= 450000 Kg displaced

450000*10 = 4500000 N upthrust.

(I'm not sure if that's correct)

If it sinks the weight of the displaced liquid is equal to the objects weight.

= 900000 Kg

900000*10 = 9000000 N

Am I on the right track?
 
If it sinks the weight of the displaced liquid is equal to the objects weight.
It is no true.

If it sinks the weight of the displaced liquid is equal to the loss of objects weight.
 
rl.bhat said:
If it sinks the weight of the displaced liquid is equal to the objects weight.
It is no true.

If it sinks the weight of the displaced liquid is equal to the loss of objects weight.

Sorry, I'm none the wiser.

Was my calculation up to that point correct?
 
In the second case, volume of the displaced liquid is...?
What is the density of the water?
What is the mass of the water and its weight?
Hence what is the upthrust?
 
Back
Top