Physics Question #25 Opted

[Aletheia]

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If someone can answer this, I would be very very grateful! 🙂

A uniform block of mass 180 g that is
10 x 9 x 3 cm is to be placed in a liquid of
density 0.900 g/cm3. The block will
A. sink in the liquid.
B. just float in the liquid with none of its
volume above the surface of the liquid.
C. float in the liquid with more than 1/2 of
its volume above the surface of the
liquid.
D. float in the liquid with less than 1/3 of its
volume above the surface of the liquid.
E. float in the liquid with all of its volume
above the surface of the liquid.

 

[loveoforganic]

buoyant force = (density of liquid)*(volume of liquid displaced)*(acceleration due to gravity)

weight = (mass block)*(acceleration due to gravity)

When weight block = buoyant force, the block floats once it is fully submerged. If weight block > buoyant force, the block sinks. If weight block < buoyant force, the block floats with just enough of the block in the water to equal the buoyant force.

 

[dontlikephysics]

That formula is all well and good but you dont know the volume of the fluid, all you are given is the mass and dimensions of the object and the density of the fluid.


You have to do Density of Object/ Density of fluid (remember, specific gravity?)

i.e.)

10 x 9 x 3 cm = 270cm3 or 2.7E2cm3

180 g/270cm3 ~ 2/3 or
~.67g/cm3 (density of object)

.67/.900 = a litte more than 2/3 or ~.64

therefore, a little more than 2/3 of the fluid is displaced so a little less than 1/3 of the object floats.

 

[Aletheia]

Thanks! That helps a ton. I certainly did not remember specific gravity, which is where I got stuck.