Physics - Study Mode

[#521] A piece of wood is held under water. The upthrust on it will be:
Correct Answer

(B) Less than weight of the wood

Explanation

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

[#522] An egg sinks in soft water but floats in a concentrated solution of salt because
Correct Answer

(C) The density of salt solution exceeds the density of eggs

Explanation

Solution: 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.

[#523] When a ship enters the sea from a river what will be the effect?
Correct Answer

(C) It rises a little

Explanation

Solution: 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.

[#524] Two identical solid pieces, one of gold and other of silver, when immersed completely in water exhibit equal weights. When weighed in air (given that density of gold is greater than that of silver)
Correct Answer

(B) The silver piece will weigh more

Explanation

Solution: 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.

[#525] When a body is immersed in a liquid, the force acting on it is
Correct Answer

(D) Both (A) and (B)

Explanation

Solution: 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.