Pressure in water and different liquid

[Scarlet_pat]

Homework Statement

consider the figures 1 and 2 which show two identical, rectangular wooden blocks

Weight of the block:

Homework Equations

Pressure = F/a
Pressure = Density x gravity x height

The Attempt at a Solution

The weight of the block,
i have tried to find the pressure of water of figure1

pressure = p g h = p = 1000 x 9.8 x 0.05 = 490 N/m^2

but i do not have any idea of what to do after.

thank you very much

 

[ashishsinghal]

There is no need for finding pressure. Find the buoyant force

 

[Scarlet_pat]

the buoyant force = V p g ...
the buoyant force = to the force exerted by the object.
therefore times the buoyant force by two, Because it is exact half submerged ?

 

[tiny-tim]

Hi Scarlet_pat!

(have a rho: ρ )

the buoyant force = V p g ...
the buoyant force = to the force exerted by the object.
therefore times the buoyant force by two, Because it is exact half submerged ?

Yes, but that's no way to prove it …

you need to write an equation, weight + buoyant force = 0.

(btw, you could have used pressure … the upward force from the water is the pressure times the area of the base … but buoyant force is more sensible )

 

[Scarlet_pat]

thank you very much for comfirming my answer :)
i was actually try to the method you have just suggested.
F= Pa = p g h * A

the the pressure there is always referring to Pressure of liquid right ?

however i think i have made a mistake ...
for F= V p g <-- the volume should be the volume of the object which submerged in the liquid right ?

 

[tiny-tim]

for F= V p g <-- the volume should be the volume of the object which submerged in the liquid right ?

(What happened to that ρ I gave you? )

I'm confused …

is ρ here the density of the block or of the water, and is this supposed to be the buoyant force or the weight?

 

[Scarlet_pat]

lets just stick to the first equation ;)
F = V p g

and what I'm wondering is F = upthrust ,
V = volume of object submerged in liquid OR volume of the block?
p = density of liquid
g = acceleration due to gravity

am i right ?

 

[tiny-tim]

The upthrust is the weight of the liquid displaced, which is the density of the liquid times the volume of the liquid displaced (ie the volume of the object submerged).

 

[Scarlet_pat]

ok thanks ... thank you. ill have to time the upthrust by 2, because the object is only half submerged ... right ?

 

[tiny-tim]

The upthrust is the upthrust, you don't "times" it by anything, you add it to the weight to get zero.

 

[Scarlet_pat]

ok thanks. :)