Question

A body of volume 100cc is immersed completely in water contained in a jar. The weight of the jar and water before immersion of the body was 700g wt. After immersion weight of the jar and the water will be
A. 700g wt.
B. 800g wt.
C. 500g wt.
D. 100g wt.

Answer 1

Hint: Here we will discuss the law of Buoyancy. If you immersed an object in a fluid or fluid like materials, the fluid would exert a force on the object upwards in reverse of its weight. This is Buoyancy.

Complete step by step answer:
The force exerted due to Buoyancy is \[v\rho g\], where v is volume of the object and \[\rho \] is density of the fluid and g is gravity of earth. While the weight or gravitational force of an object is mg=vdg, where m is mass of the object, v is volume of the object and d is density of the object and g is gravitational acceleration of earth. The net for acting on an object while placing on a fluid is \[v\rho g-vdg\]. For a fully immersed object this force is exactly equal to zero, because there is no net force acting on the object. This also means for an object to immerse completely, the weight of the object and force due to buoyancy is equal.
In our case, the object is fully immersed. So, there will be no additional force acting downward as weight, due to complete immersion of the object. So, It will be exactly the same weight as the water and jar without the object immersing itself in the water.
The correct answer of this question is option A.

Note:
Fluid like objects are mentioned, because there are some systems that show exactly the same properties like a fluid though it is not fluid. The examples will be air, plasma etc. Nowadays, fluidity is an important subject to study in research fields.