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Krishna is trying to push an empty air tight bottle into a beaker full of water. As he tries to push it further down:

Krishna is trying to push an empty air tight bottle into a beaker full of water. As he tries to push it further down: Correct Answer he needs to apply more force

CONCEPT:

  • Archimedes' principle states that when a body immersed in a fluid, whether fully or partially submerged, the upward buoyant force that is exerted on it, is equal to the weight of the fluid that the body displaces.
    • When an object is submerged in fluid fully or partially, an upward force is exerted on the body. This force is known as the buoyant force.

 Fbuoyant = ρf Vf g 

where ρf is the density of the fluid in which the object is submerged, Vf is the volume of the displaced fluid (or volume of the object that is submerged inside the fluid)  and g is the gravitational acceleration.

  • When an object is submerged in fluid fully or partially there are two forces, 1. buoyant force 2. weight of the object 

and weight of object W = mg = ρo Vo g    where ρo is the density of the object, Vo is the volume of the object, g is the gravitational acceleration.

  • Laws of Floatation: The three conditions required for the body to float on water are:

  1. The weight of the body in the figure is equal to the buoyant force. (c) (d)

  2. The weight of the body is greater than the weight of the fluid displaced i.e. buoyant force.  (b)

  3. The weight of the body is less than the weight of the fluid displaced i.e. buoyant force. (a)

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EXPLANATION:

Fbuoyant = ρf Vf g 

where ρf is the density of the fluid in which the object is submerged, Vf is the volume of the displaced fluid (or volume of the object that is submerged inside the fluid)  and g is the gravitational acceleration.

  • When an object is submerged in a fluid/liquid, the buoyancy force depends on the volume of the liquid displaced. 
  • As Krishna pushes the bottle down in the water, the volumes of the displaced water increases, and the force of buoyancy increases and hence he needs to apply more force. So option 1 is correct.

[ alt="MISTAKE POINT" src="//storage.googleapis.com/tb-img/production/20/06/MISTAKE%20POINT.png" style="width: 151px; height: 45px;"> 

  • It is to remember that while calculating the buoyant upward force, we take the density of the liquid (not the density of the object).

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