Advertisements
Advertisements
Question
Explain the following :
A balloon filled with hydrogen rises to a certain height and then stops rising further.
Advertisements
Solution 1
The reason is that the density of air decreases with altitude. Therefore, as the balloon gradually goes up, the weight of the displaced air (i.e. uphrust) decreases. It keeps on rising as long as the upthrust exceeds its weight. When upthrust becomes equal to its weight, it stops rising.
Solution 2
A balloon filled with hydrogen has low density than air so it rises over the air but as height increases density of air decreases and at a certain height the density of hydrogen in balloon and density of air become equal. And as there is no density difference there is no pressure difference also and hence balloon stops rising further.
RELATED QUESTIONS
A body dipped into a liquid experiences an upthrust. State two factors on which upthrust on the body depends.
A body held completely immersed inside a liquid experiences two forces:
(i) F1, the force due to gravity and
(ii) F2, the buoyant force.
Draw a diagram showing the direction of these forces acting on the body and state the condition when the body will float or sink.
A body of volume 100 cm3 weighs 5 kgf in air. It is completely immersed in a liquid of density 1.8 × 103 kg m-3. Find:
- The upthrust due to liquid and
- The weight of the body in liquid.
A piece of brass weighs 175 gf in air and 150 gf when fully submerged in water. The density of water is 1.0 g cm-3.
(i) What is the volume of the brass piece? (ii) Why does the brass piece weigh less in water?
How does the density ρs of a substance determine whether a solid piece of that substance will float or sink in a given liquid ρL?
A man first swims in sea water and then in river water. (i) Compare the weights of sea water and river water displaced by him.
(ii) Where does he find it easier to swim and why?
A rubber ball floats on water with its 1/3rd volume outside water. What is the density of rubber?
If the density of ice is 0.9 g cm-3, then what portion of an iceberg will remain below the surface of water in sea? (Density of sea water = 1.1 g cm-3)
A solid body weighs 2.10 N. in air. Its relative density is 8.4. How much will the body weigh if placed
(1) in water,
(2) in liquid of relative density 1.2?
