Problem of fluid -- Blocks, pulley, two fluids

In summary: I included the fluid in the gap between block 1 and block 2 in my force balance.In summary,Chet tried to do a force balance on two blocks, but his calculations didn't work out the same. He needs to include the fluid in the gap between the blocks in his calculations in order to get accurate results.
  • #1
Queren Suriano
50
0

Homework Statement


dynamic viscosity 1 = 1125 2 kgf-s / m2 , dynamic viscosity 2 = 62.5 2 kgf-s / m2 , Areas: A1 = 20 cm2 , A2 = 50 cm2
W1 = 15 Kgf, W2 = 40 Kgf.
The block (2) is displaced downwards with a
constant speed of 80 mm / sec, whereas
linear velocity distribution determined:
1) The weight of the block (3).
2) The speed of the block (1).
Neglect friction in the pulley
upload_2015-3-3_12-13-33.png

upload_2015-3-3_12-25-39.png


Homework Equations


the angle is 30º
(tangencial force) / area = (dynamic viscosity) (velocity/space betwteen the two surfaces)

sum forces=0 (Equilibrium)

The Attempt at a Solution



I did the problem of two ways, considering each block and considering the system, but I don't get the same answer.

What am I doing wrong??
 
Last edited:
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  • #2
Your force balance on block 2 is incorrect, and your force balance on the overall system is incorrect. Your calculated value of F2 is correct. The force balance for the overall system should be the sum of the force balances on the individual blocks.

Chet
 
  • #3
I don't understand why the force balance on block 2 is incorrect?? Because in the block 2 acts two tangetial forces due the fluid, and the component horizontal of the weight
 
  • #4
Queren Suriano said:
I don't understand why the force balance on block 2 is incorrect?? Because in the block 2 acts two tangetial forces due the fluid, and the component horizontal of the weight
It should include only the component of the weight of block 2, not both blocks.

Chet
 
  • #5
Chestermiller said:
It should include only the component of the weight of block 2, not both blocks.

Chet
But the block 2 support the block 1, if I only consider the weight of block 2, it's just like the block 2 was alone, but it doesnt
 
  • #6
Queren Suriano said:
But the block 2 support the block 1, if I only consider the weight of block 2, it's just like the block 2 was alone, but it doesnt
The weight of block 1 exerts a force on block 2 in the normal direction, but block 1 is not exerting a force on block 2 in the tangential direction. The fluid in the gap between block 1 and block 2 is exerting a force on block 2 in the tangential direction, but you've already included that in your force balance.

Chet
 

1. What is the problem of fluid in blocks and pulleys?

The problem of fluid in blocks and pulleys refers to a common scenario in physics where two or more blocks are connected by a rope or a pulley system and are immersed in fluids, such as water or oil. This problem involves finding the equilibrium state of the system, taking into account the effects of fluid pressure, buoyancy, and viscosity.

2. How do you calculate fluid pressure in this problem?

To calculate fluid pressure in this problem, you need to use the equation P = ρgh, where P is the pressure, ρ is the density of the fluid, g is the acceleration due to gravity, and h is the height of the fluid column. This equation applies to both stationary and moving fluids, and can be used to determine the pressure at any point in the system.

3. What is the role of buoyancy in the problem of fluid in blocks and pulleys?

Buoyancy is a crucial factor in this problem, as it determines the upward force exerted by the fluid on the objects immersed in it. This force counteracts the weight of the objects and affects their equilibrium state. The buoyant force is equal to the weight of the fluid that is displaced by the objects.

4. How does viscosity impact the behavior of fluids in this problem?

Viscosity is the measure of a fluid's resistance to flow. In the problem of fluid in blocks and pulleys, viscosity affects the movement of the fluid and the objects immersed in it. High viscosity fluids, such as honey, will result in slower movement and more resistance, while low viscosity fluids, such as water, will result in faster movement and less resistance.

5. Are there any real-world applications of this problem?

Yes, this problem has many real-world applications, such as in fluid mechanics, hydraulics, and engineering. Understanding the behavior of fluids in blocks and pulleys is crucial in designing and optimizing machinery and systems that involve fluid flow. It is also relevant in fields such as automotive and aerospace engineering, where fluid dynamics play a significant role in the design and operation of vehicles.

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