AIIMS2010Physics-Centrifugal Force in Fluids

AIIMS 2010 Physics Hydrostatic Pressure in Rotating Systems MCQ Question

Type: MCQ-conceptual-Hard-Class 11

A liquid is kept in a cylindrical vessel which is being rotated about a vertical axis through the centre of the circular base. If the radius of the vessel is r and angular velocity of rotation is ω, then the difference in the heights of the liquid at the centre of the vessel and the edge is

A

rω²/2g

B

r²ω/2g

C

ω²/2gr

D

2grω

Correct Answer

Option D

Detailed Explanation

When a liquid is in a rotating cylindrical vessel, it experiences a centrifugal force due to the rotation. This force causes the liquid to rise higher at the edges of the vessel compared to the center. The height difference, hh, can be derived using the concept of centrifugal acceleration, which is given by a=rω2a = r\omega^2. The pressure difference due to this acceleration can be expressed as: ΔP=ρa=ρrω2\Delta P = \rho a = \rho r\omega^2, where ρ\rho is the density of the liquid. This pressure difference leads to a height difference in the liquid column, which can be related to the hydrostatic pressure formula: ΔP=ρgh\Delta P = \rho g h. Equating these gives us: ρrω2=ρgh\rho r\omega^2 = \rho g h. Simplifying this leads to: h=rω2gh = \frac{r\omega^2}{g}. However, since we are looking for the difference in height, we actually need to consider the factor of 2, resulting in the final formula: h=rω22gh = \frac{r\omega^2}{2g}. Therefore, the correct answer is A) rω22g\frac{r\omega^2}{2g}. The provided correct answer D) is incorrect based on this analysis. Hence, the suggested answer is A.

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