Question about Elastic force and Buoyancy force

Click For Summary
SUMMARY

The discussion centers on calculating the elastic force of a spring connected to a wooden cube submerged in water. The wooden cube has a side length of 10 cm and a density of 0.6 g/cm³, while the water has a density of 1 g/cm³. The correct elastic force is determined to be 4N, derived from the buoyancy force of 10N minus the weight of the cube, which is 6N. The confusion arises from misinterpretations of buoyancy and weight relationships in the context of the problem.

PREREQUISITES
  • Understanding of buoyancy principles and Archimedes' principle
  • Knowledge of spring force calculations
  • Familiarity with density and weight calculations
  • Basic physics concepts related to fluid mechanics
NEXT STEPS
  • Study Archimedes' principle and its applications in fluid mechanics
  • Learn about spring force calculations and Hooke's Law
  • Explore density calculations and their implications in buoyancy
  • Investigate the relationship between pressure and buoyancy in fluids
USEFUL FOR

Students preparing for physics exams, educators teaching fluid mechanics, and anyone interested in understanding the principles of buoyancy and spring forces in physics.

MatinSAR
Messages
673
Reaction score
204
Homework Statement
Elastic force and Buoyancy force
Relevant Equations
Archimedes' principle
Suppose a wooden cube with a side of 10 cm is connected to the bottom of a water container by a spring. If the density of wood is 0.6g/cm^3 and the density of water is 1g/cm^3 , what is the elastic force of the spring? Is it 4N or 6N ?

I think the answer is 4N … But the book says it is 6N , Could you please guide me which one is correct ?!

My answer : Spring force = Buoyancy force - Weight of the cube = 10N - 6N = 4N
 
Physics news on Phys.org
MatinSAR said:
My answer : Spring force = Buoyancy force - Weight of the cube = 10N - 6N = 4N
Your thinking looks good to me. (Did the book provide a solution or just the answer?)
 
  • Like
Likes   Reactions: MatinSAR
Doc Al said:
Your thinking looks good to me. (Did the book provide a solution or just the answer?)
Thank you for your answer.
It said the Spring force is equal to the Buoyancy force that acts on wooden cube and this Buoyancy force is equal to the weight of the cube due to complete submersion in water …
 
MatinSAR said:
... this Buoyancy force is equal to the weight of the cube due to complete submersion in water …
Something is not correct about this last statement.
The weight of what cube?
 
  • Like
Likes   Reactions: MatinSAR
Lnewqban said:
Something is not correct about this last statement.
The weight of what cube?
We have only one wooden cube in the question and the weight of the cube is 6N.
 
MatinSAR said:
It said the Spring force is equal to the Buoyancy force that acts on wooden cube
That's not right. (It ignores the weight of the cube.)
MatinSAR said:
and this Buoyancy force is equal to the weight of the cube due to complete submersion in water
That's also not quite right (as @Lnewqban points out).

What book are you using?
 
  • Like
Likes   Reactions: Lnewqban
MatinSAR said:
We have only one wooden cube in the question and the weight of the cube is 6N.
There was a heavier cube originally ocupying the volume of our unique and now submerged wooden cube.
 
Last edited:
  • Like
Likes   Reactions: MatinSAR
Doc Al said:
That's not right. (It ignores the weight of the cube.)
Thank you …
Doc Al said:
What book are you using?
It's not a reference book like Fundamentals of Physics or …
It was a kind of school book for being ready for the tests and exams …
Lnewqban said:
There was a cube originally ocupying the volume of our unique and now submerged wooden cube.
I'm sorry but I don't understand … Do you mean 6N is false ?!
 
MatinSAR said:
... I'm sorry but I don't understand … Do you mean 6N is false ?!
Please, see:
https://en.m.wikipedia.org/wiki/Buoyancy

The buoyancy effect is generated by the weight of the fluid that has been displaced by the volume of the fully submerged wooden cube.
The fluid surrounding the solid is puting pressure on it, trying to regain that volume.

Think of the cube as a piston of wood pushing down and a piston of water pushing up, only that harder, in the same ratio in which the densities of water and wood differ.

It is only about the statement of post # 3 above, your answer is good.
 
Last edited:
  • Like
Likes   Reactions: MatinSAR
  • #10
Lnewqban said:
It is only about the statement of post # 3 above, your answer is good.
Thank you.
 
  • Like
Likes   Reactions: Lnewqban

Similar threads

Buoyancy and the Archimedes Principle
  • · Replies 6 ·
Replies
6
Views
2K
Buoyancy force when a ramp is under water
  • · Replies 15 ·
Replies
15
Views
2K
How to Calculate Upward Force on Each Anchorage?
  • · Replies 3 ·
Replies
3
Views
2K
Calculating Buoyancy Force & Length of Submerged Cube
  • · Replies 11 ·
Replies
11
Views
3K
Force on the bottom of the vessel containing a submerged cube
  • · Replies 30 ·
2
Replies
30
Views
4K
Forces applied to a spring-loaded gas pedal
  • · Replies 7 ·
Replies
7
Views
1K
What is the spring's length and constant in Hooke's law with buoyancy force?
  • · Replies 2 ·
Replies
2
Views
2K
Multiple choice buoyancy problem
  • · Replies 6 ·
Replies
6
Views
2K
Density of Liquid: 1667.7kg/m^3 | Solving Buoyancy Q.
  • · Replies 8 ·
Replies
8
Views
3K
Understanding Buoyancy: Solving a Simple Cube Floating Question
  • · Replies 1 ·
Replies
1
Views
2K