Question

If a ball of steel (density $$\rho = 7.8\,g\,c{m^{ - 3}}$$   ) attains a terminal velocity of $$10\,cm{s^{ - 1}}$$  when falling in a tank of water (coefficient of viscosity $${\eta _{{\text{water}}}} = 8.5 \times {10^{ - 4}}\,Pa - s$$     ) then its terminal velocity in glycerine $$\left( {\rho = 12\,g\,c{m^{ - 3}},\eta = 13.2\,Pa - s} \right)$$       would be nearly

A. $$1.6 \times {10^{ - 5}}cm{s^{ - 1}}$$
B. $$6.25 \times {10^{ - 4}}cm{s^{ - 1}}$$  
C. $$6.45 \times {10^{ - 4}}cm{s^{ - 1}}$$
D. $$1.5 \times {10^{ - 5}}cm{s^{ - 1}}$$
Answer :   $$6.25 \times {10^{ - 4}}cm{s^{ - 1}}$$
Solution :
$$\eqalign{ & v \propto \frac{{\rho - {\rho _0}}}{\eta } \cr & \therefore \frac{{{v_2}}}{{{v_1}}} = \frac{{\rho - {\rho _{02}}}}{{\rho - {\rho _{01}}}} \times \frac{{{\eta _1}}}{{{\eta _2}}} = \frac{{7.8 - 1.2}}{{7.8 - 1}} \times \frac{{8.5 \times {{10}^{ - 4}} \times 10}}{{13.2}} \cr & = 6.25 \times {10^{ - 4}}\,cm{s^{ - 1}} \cr} $$

Releted MCQ Question on
Basic Physics >> Mechanical Properties of Solids and Fluids

Releted Question 1

The following four wires are made of the same material. Which of these will have the largest extension when the same tension is applied?

A. $$length=50\,cm, \,\,diameter=0.5 \,mm$$
B. $$length = 100 \,cm, \,\,diameter= 1 \,mm$$
C. $$length= 200 \,cm, \,\,diameter= 2 \,mm$$
D. $$length=300 \,cm, \,\,diameter =3 \,mm$$
Releted Question 2

A U-tube of uniform cross section (see figure) is partially filled with a liquid I. Another liquid II which does not mix with liquid I is poured into one side. It is found that the liquid levels of the two sides of the tube are the same, while the level of liquid I has risen by $$2 \,cm.$$  If the specific gravity of liquid I is $$1.1,$$  the specific gravity of liquid II must be-
Mechanical Properties of Solids and Fluids mcq question image

A. $$1.12$$
B. $$1.1$$
C. $$1.05$$
D. $$1.0$$
Releted Question 3

A homogeneous solid cylinder of length $$L\left( {L < \frac{H}{2}} \right),$$   cross-sectional area $$\frac{A}{5}$$ is immersed such that it floats with its axis vertical at the liquid-liquid interface with length $$\frac{L}{4}$$ in the denser liquid as shown in the figure. The lower density liquid is open to atmosphere having pressure $${P_0}.$$ Then density $$D$$ of solid is given by-
Mechanical Properties of Solids and Fluids mcq question image

A. $$\frac{5}{4}d$$
B. $$\frac{4}{5}d$$
C. $$4d$$
D. $$\frac{d}{5}$$
Releted Question 4

A large open tank has two holes in the wall. One is a square hole of side $$L$$ at a depth $$y$$ from the top and the other is a circular hole of radius $$R$$ at a depth $$4y$$  from the top. When the tank is completely filled with water, the quantities of water flowing out per second from both holes are the same. Then, $$R$$ is equal to-

A. $$\frac{L}{{\sqrt {2\pi } }}$$
B. $$2\pi L$$
C. $$L$$
D. $$\frac{L}{{2\pi }}$$

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