Three objects, same size, diff density, submerged in water

[libraryismyhome]

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wow...

Three objects are placed in a tank of water. The objects all have the same size, but they have diff densities: p1 < p2 < p3. All of the densities are less than the density of water. If all the objects are released at the same time, which object reaches the surface first??


So my reasoning was...
Same size means same volume. So the object 3 has the greatest mass, and it exerts the greatest downward force. F=mg

I assumed that the buoyancy force would be same for all, so I thought object 3 would reach the surface first because Fnet = F-B. But the answer is object 1. 😱

 

[attixx]

Well first think about it from an intuitive approach.

An object floats because it is less dense than water. The less dense it is, the easier it would float so it would make sense that it would reach the top first.


F(bouyancy) - mg = ma:
Fb is the same for all three since the volumes are all the same, and they are all in the same body of water so the density of the liquid is all the same (and of course gravity).

The less dense object will have the lowest mass per its volume. So in the equation if m is smaller, a will be bigger.

a=[F(bouyancy) - mg]/m = a

 

[libraryismyhome]

Well first think about it from an intuitive approach.

An object floats because it is less dense than water. The less dense it is, the easier it would float so it would make sense that it would reach the top first.


F(bouyancy) - mg = ma:
Fb is the same for all three since the volumes are all the same, and they are all in the same body of water so the density of the liquid is all the same (and of course gravity).

The less dense object will have the lowest mass per its volume. So in the equation if m is smaller, a will be bigger.

a=[F(bouyancy) - mg]/m = a

Thank you so much!! 👍👍