BUOYANCY

Some question (Assertion-Reason type) are given below. Each question contains STATEMENT-1(Assertion) and STATEMENT-2(Reason) . Each question has 4 choices (A),(B),(C ) and (D) out of which ONLY ONE is correct. So select the correct choice : STATEMENT-1 1kg of cotton fibre will weight less lens in air when made more fluffy. STATEMENT-2 Weight of air in cotton will cancel out with the force of extra buoyancy acting on it.

Statement I: A needle placed carefully on the surface of water may float, whereas the ball of the same material will always sink. Statement II: The buoyancy of an object depends both on the material and shape of the object.

Let T represent the true weight of a body, B the force of buoyancy on the body when immersed in a liquid. A represents the apparent weight of the body and W be twice the weight of liquid displaced by te body. Then which of the following relation is correct?

A cylindrical block is floating (partially submerged) in a vessel containing water. Initially, the platform on which the vessel is mounted is at rest. Now the platform along with the vessel is allowed to fall freely under gravity. As a result, the buoyancy force

A hot air balloon (mass M) has a passenger (mass m) and is stationary in the mid air. The passenger climbs out and slides down a rope with constant velocity u relative to the balloon. (a) Show that when the passenger is sliding down, there is no change in mechanical energy (kinetic + gravitational potential energy) of the system (Balloon + passenger). Calculate the speed of balloon. (b) Calculate the power of the buoyancy force on the system when the man is sliding. For easy calculation, assume that volume of man is negligible compared to the balloon. (c) If buoyancy force is doing positive work, where is this work done lost? You have proved that sum of kinetic and potential energy of the system remains constant

Which of the following statement are not true about shark? a. The skin is tough and covered with placoid scales. b. They possess a swim bladder which regulates buoyancy. c. the tail of shark is heterocercal. d. Ampulla of lorenzini present in the snout of shark is thermoreceptor. e. it has five pairs of gill slits covered by operculum.