Practice MCQ Questions and answers on Physics-GK

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.

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.

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.

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.

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.

Since wooden piece is to float on water, upthrust acting on it under water is greater than the weight of the wooden piece.

Following the density principle, the density of the egg compared to the density of the tap water is lesser (the density principle states that an object or substance with lesser density will float on the surface of the substance or object which has the greater density). Now, with salt, salt makes the density of the tap water to increase and increases also the salinity of the water making the egg float because the density of the water with salt is now greater than the density of the egg and that is why an egg sinks in soft water but floats in a concentrated solution of salt.

When a ship enters a sea from a river, the ship is elevated or uplifted due to the density of sea water and during the buoyant motion of the ship, as it would gain both potential and kinetic energy when rising in the fluid.

As it is said that density of gold is greater than that of density of silver, so silver occupies a greater volume than gold. So it has more upthrust from the water, although they both show the same weight under water, there is more silver present. Hence silver piece will weigh more.

According to the Principle of Flotation, when a body is immersed in a fluid, two forces act on it: (1) The weight of the body acting vertically downward through the centre of gravity of the body, and (2) The upthrust of the fluid acting vertically upward through the centre of gravity of the fluid displaced, i.e., centre of buoyancy. The upthrust is also termed as buoyant force.