Physics - Study Mode

[#516] A hydrogen balloon floats up because of
Correct Answer

(C) Weight of the balloon is less than the weight of air displaced by it.

Explanation

Solution: The balloon has to displace some air, so in response, the air pushes up on it. But hydrogen is less dense than air, so the air pushes up on the balloon harder than gravity is pulling it down, and the balloon tries to move up. So just like wood float on water, hydrogen balloons float on air.

[#517] A boat will submerge when it displaces water equal to its own:
Correct Answer

(B) Weight

Explanation

Solution: A boat will float when the weight of the water it displaces equals the weight of the boat and anything will float if it is shaped to displace its own weight of water before it reaches the point where it will submerge.

[#518] What is the principle of a ''Life Jacket"?
Correct Answer

(B) It increases the volume of the person to keep him afloat

Explanation

Solution: The upward-pushing force that keeps things afloat is called buoyancy. For an object to float it must be able to equal its own weight by displacing enough water. A life jacket is mainly filled with gas which has a very low mass. As such when worn by a person, it acts to significantly increase their volume for only a very small increase in their mass. This means that they have a lower density than normal which increases their buoyancy and helps them to float.

[#519] When a piece of stone is immersed in water, it displaces water of equal
Correct Answer

(C) Mass

Explanation

Solution: Archimedes’ Principle states that upward buoyant force exerted on a body immersed in a fluid is equal to the weight of the fluid the body displaces.

[#520] It is easier for a man to swim in sea water, than in river water because
Correct Answer

(B) The density of sea water is more than the density of river water

Explanation

Solution: It is easier for a man to swim in sea water, than in river water because sea water contains more amount of salt as compared to river/fresh water as a result its density increases and hence the buoyant force increases which makes it easier to swim in sea water.