﻿ The Poisson s ratio of a material is 0.5. If a force is applied t

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# 11.The Poisson's ratio of a material is 0.5. If a force is applied to a wire of this material, there is a decrease in the cross-sectional area by 4%. The percentage increase in the length is1 % 2 % 2.5 % 4 %

D.

4 %

Poisson ratio = 0.5

Since, density is constant therefore change in volume is zero, we have

V = A × l = constant

⇒  log V = log A + log l

∴   Percentage increase in length = 4%

12.

Two spheres of equal masses but radii r1 and r2 are allowed to fall in a liquid of infinite column. The ratio of their terminal velocities is

• 1

• r1 : r2

• r2 : r1

13.

Two massless springs of force constants k1 and k2 are joined end to end. The resultant force constant k of the system is

14.

A spring of force constant k is cut into two equal halves.  The force constant of each half is

• $\frac{\mathrm{k}}{\sqrt{2}}$

• k

• $\frac{\mathrm{k}}{2}$

• 2k

15.

Two rods of equal length and diameter have thermal conductivities 3 and 4 units respectively. If they are joined in series, the thermal conductivity of the combination would be

• 3.43

• 3.5

• 3.4

• 3.34

16.

19 g of water at 30°C and 5 g of ice at -20°C are mixed together in a calorimeter. What is the final temperature of the mixture ? (Given specific heat of ice = 0.5 cal g-1 (C)-1 and latent heat of fusion of ice = 80 cal g-1)

• 0°C

• − 5°C

• 5°C

• 10°C

17.

It is difficult to cook rice in an open vessel by boiling it at high altitudes because of

• low boiling point and high pressure

• high boiling point and low pressure

• low boiling point and low pressure

• high boiling point and high pressure

18.

The height of a waterfall is 50 m. If g = 9.8 ms-2 the difference between the temperature at the top and the bottom of the waterfall is

• 1.17°C

• 2.17°C

• 0.117°C

• 1.43°C

19.

The equation of state for n moles of an ideal gas is pV = nRT, where R is a constant. The SI unit for R is

• Jk-1 per molecule

• JK-1 mol-1

• JKg-1K-1

• Jk-1g-1

20.

One kg of copper is drawn into a wire of 1 mm diameter and a wire of 2 mm diameter. The resistance of the two wires will be in the ratio

• 2 : 1

• 1 : 2

• 16 : 1

• 4 : 1