A body floats in a liquid contained in a beaker. The whole system as shown in Figure falls freely under gravity. The upthrust on the body is

Options

A. equal to the weight of the body in air
B. equal to the weight of the body in air
C. zero
D. equal to the weight of the immeresed part of the body

Answer

A

Explanation

Upthrust is independent of all factors of the body such as its mass, size and density, etc. except the volume of the body inside the fluid. Fraction of volume immersed in the liquid `V_("in") = ((rho)/(sigma))V`, i.e. it depends upon the densities of the block and liquid. So, there will be
no change in it if system moves upward or downward with constant velocity of same acceleration. Therefore, the upthrust on the body due to liquid is equal to the weigth of the body is air.