The velocity of a small ball of mass \(\mathrm{m}\) and density \(\mathrm{d}_{1}\) when dropped in a container filled with glycerine becomes constants after sometime. What is the viscous force acting on the ball ? (density of glycerine is \(\mathrm{d}_{2}\) ) (A) \(m g\left\\{1-\left(d_{1} / d_{2}\right)\right\\}\) (B) \(m g\left\\{1-\left(d_{2} / d_{1}\right)\right\\}\) (C) \(m g\left\\{d_{1} /\left(d_{1}-d_{2}\right)\right\\}\) (D) $\operatorname{mg}\left\\{\mathrm{d}_{2} /\left(\mathrm{d}_{1}-\mathrm{d}_{2}\right)\right\\}$

Short Answer

Expert verified
(A) \(mg\\ \{1 - (d_1 / d_2)\\}\)

Step by step solution

01

Identifying the forces acting on the ball

When the ball is moving through the glycerine, it experiences three forces: 1. Gravitational force (weight) = mg, acting downward 2. Buoyant force = the upward force due to the displacement of glycerine, given by \(V \times d_2 \times g\), where V is the volume of the ball 3. Viscous force = the force due to the glycerine acting upward and opposite to the motion of the ball
02

Finding the terminal velocity

Terminal velocity occurs when the net force acting on the ball becomes zero, and the ball moves with a constant velocity. At terminal velocity, the sum of the buoyant force and the viscous force equals the gravitational force acting on the ball. So, we have: Buoyant force + Viscous force = Gravitational force
03

Expressing the forces in terms of mass and density

The volume V of the ball can be expressed as \(V = \frac{m}{d_1}\), where m is the mass of the ball and \(d_1\) is its density. Using this, we can rewrite the equation from Step 2 as: \(\frac{m}{d_1} \times d_2 \times g\) + Viscous force = mg
04

Solving for the viscous force

Rearrange the equation in Step 3 to find the expression for the viscous force: Viscous force = mg - \(\frac{m}{d_1}\) × \(d_2g\) Now, factor out the mg term to simplify: Viscous force = mg\(\\ \{1 - (d_1 / d_2)\\}\) Comparing this expression with the given options, we see that it matches option (A). Therefore, the viscous force acting on the ball is
05

(A) \(mg\\ \{1 - (d_1 / d_2)\\}\)

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Most popular questions from this chapter

A steel ball of diameter \(3 \mathrm{~mm}\) falls through glycerine and covers a distance of \(25 \mathrm{~cm}\) in \(10 \mathrm{~S} .\) The specific gravity of steel and glycerine are \(7.8\) and \(1.26\) respectively. The viscosity of glycerine is about........ pascal-sec (A) \(1.3\) (B) \(1.5\) (C) \(0.8\) (D) \(1.0\)

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