Question

I.Give reasons for the following: 1) Equal masses of different substances have different volumes. 2)Equal volumes of different substances have different masses. 3)The lower end of a hydrometer is filled with mercury or lead. 4)Bodies like cork or wood float on water. 5)An iron needle sinks in water, but an iron ship floats on water.

Answer 1

Explanations:

1) Equal masses of different substances may have different volumes as the    density of each substance is different and volume = Mass/Density.

Ex: Equal mass of cotton and iron have different volumes as iron is more dense iron has a less volume.

2) It's the same reason for the first Equal volumes of different substances may have different masses as the density of each substance is different and Mass = Density * Volume.

Ex: The same volume of iron and cotton have different mass as cottons density is less its mass will also be less.

3)The lower end of the Hydrometer is filled with mercury or lead because it  lowers the center of gravity of the hydrometer so that it remains in a stable equilibrium and floats in an upright position.

4)Materials like cork and wood float on water as their density is less than of water. The density of water is 1 g/cm^3 but for cork is 0.2 to 0.25 g/cm^3 and for wood is 0.6 to 0.9 g/cm^3.

5) An iron needle sinks in water as its surface area touching the water is less and it needs to make more contact of its surface area as it's density is more than waters whereas in an iron boat the surface area touching the water is enough to make the boat float in water.

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Answer 2

Reasons for the following:

1. Equal masses of different substance have different volumes because volume is the ratio of mass and density and their their density varies. Therefore, with change in density volume also changes with it.
2. Equal volumes of different substances have different masses because they may have closely or loosely packed atoms and also different densities.
3. The lower end of a hydrometer is filled with mercury or lead because they are moldable and cheaper in cost. Also, they keep the hydrometer heavy so it stays upright.
4. Bodies like wood or cork float on water because they have densities less than that of water.
5. Weight of an iron nail is more than weight of water displaced by the nail so it sinks in water. While on the other hand the shape of the iron ship is made in such a way that it displaces less weight in the water than its own weight.

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