Fluid Statics - net upward force

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SUMMARY

The discussion centers on calculating the net upward force on a cube submerged in a liquid, specifically deriving the relationship between depth (h), mass (m), density (ρ), and side length (l) of the cube. The net force (Fn) is established as Fn = ρlg, where ρ is the liquid's density, l is the cube's side length, and g is the acceleration due to gravity. The confusion arises regarding the variable h, which is clarified to represent the depth of the cube when it is floating, rather than the initial depth (h0). The conclusion drawn is that h can be expressed as h = m/ρl², linking the cube's mass to its submerged depth.

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Roodles01
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Homework Statement


Find magnitude of net upward force on a cube in terms of l, ρ (rho), g and h. then show that h = m/ρl2

A solid cube, mass m, side length l, is placed in a liquid of uniform density, ρ(rho), at a depth h0 below the surface of the liquid, which is open to the air.
The upper and lower faces of the cube are horizontal.

(this is from previous question https://www.physicsforums.com/threads/force-exerted-by-fluid.784711/)

Homework Equations


pressure, p = ρ g h
mass = ρ x volume of liquid displaced

The Attempt at a Solution


Net force, Fn = (pbottom x area of cube face) - (ptop x area of cube face)
p at top face = (pT) x ρliquid x h x g
p at bottom face = (pB) x ρliquid x (h+l) x g
so
Fn = (ρgh + ρlg - ρgh)
Fn = ρlg

Net force - fine.
Er! how do I show that h = m/ρl2
I know m = ρ x v . . .
 
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Roodles01 said:
Er! how do I show that h = m/ρl2
I can only make sense of the question if h is different from h0. (Your working all has h, but the question used h0.)
A reasonable meaning for h would be that the block is released and floats level with depth h immersed.
 
haruspex said:
I can only make sense of the question if h is different from h0. (Your working all has h, but the question used h0.)
A reasonable meaning for h would be that the block is released and floats level with depth h immersed.

I have looked at the question and unscrewed the bits of paper I attempted my answers on and the h0 seems to be a complete typo, it all says just plain h. I will try to work through with that in mind, as you say.
 

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