What is a submarine? How can it be made to dive in water and come to the surface of water?

A balloon filled with hydrogen rises in air. Explain the reason.

Which of the following will sink or float on water? (Density of water = 1 g cm^-3)

1. Body A having density 500 kg m^-3
2. Body B having density 2520 kg m^-3
3. Body C having density 1100 kg m^-3
4. Body D having density 0.85 g cm^-3

The density of water is 1.0 g cm^-3. The density of iron is 7.8 g cm^-3. The density of mercury is 13.6 g cm^-3. Answer the following:

(a) Will a piece of iron float or sink in water?

(b) Will a piece of iron float or sink in mercury?