Hi. i\'m a bit confused about mass fluid displaced, weight fluid displaced, buoy

Question

Hi. i'm a bit confused about mass fluid displaced, weight fluid displaced, buoyant forces, etc.

Lets say I have a wood block (mass = 2kg, density = 0.40kg/L) and brick block (mass=16kg and density=2kg/L). The fluid in which I put these blocks in is just water (density = 1kg/L) and the total amount of water I have is 100L.

The wooden block floats, because it is less dense than water. The brick block sinks because it has a higher density than water.

What would be the volume of fluid displaced for the wooden and brick blocks? (in m^3)

What about the mass of fluid displaced (in kg), and the weight of the fluid displaced (in Newtons) for each block?

Please help. I'm so confused.

My attempt:

The volume of the wood block would be = 5m^3, and volume of brick block = 8m^3

(found by using density=mass/volume equation.

Does that mean the volume of fluid displaced by....

a) wood block = 2m^3

b) brick block = 8m^3 ??

Also, is this true?:

for a floating object in a liquid, the weight of liquid displaced is = weight of object (mass object x gravity)

please help. and also please try to keep things simple. :( Also, please answer the above question but leave an explanation!

thanks a bunch!!

Explanation / Answer

Let us say volume of fluid displaced for the wooden = V

as the brick is floating , the mass of fluid displaced = mass of wooden block

so V* density of water = mass of wooden block

V * 1 = 2

V = 2/1 = 2 L

volume of fluid displaced for the wooden = V = 2L = 0.002 m^3 ( as 1 L = 0.001 m^3)

As the brick completely sinks ,

volume of fluid displaced for the brick = volume of brick = mass of brick / density of brick = 16/2 = 8 L = 0.008 m^3

In case of wooden block , mass of fluid displaced = mass of wooden block = 2 Kg.

weight of fluid displaced for wooden block = mass * acceleration due to gravity = 2*9.8 = 19.6 N

In case of brick , mass of fluid displaced = volume of fluid displaced * density of fluid = 8 * 1 = 8 Kg

weight of fluid displaced for brick = mass * acceleration due to gravity = 8*9.8 = 78.4 N

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