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21.

Choose the wrong statement

The bulk modulus for solids is much larger than for liquids

Gases are least compressible

The incompressibility of the solids is due to the tight coupling between neighbouring atoms

The reciprocal of the bulk modulus is called compressibility

22.

Identify the incorrect statement.

Young's modulus and shear modulus are relevant only for solids.

Bulk modulus is relevant for solids, liquids and gases.

Alloys have larger values of Young's modulus than metals.

Metals have larger values of Young's modulus than elastomers

23.

A lead bullet strikes against a steel plate with a velocity 200 ms^{-1}. If the impact is perfectly inelastic and the heat produced is equally shared between the bullet and the target, then the rise in temperature of the bullet is (Specific heat capacity of lead = 125 J Kg^{-1} K^{-1})

80°C

60°C

160°C

40°C

24.

Which one of the following statements is correct? In the case of

shearing stress there is change in volume

tensile stress there is no change in volume

shearing stress there is no change in shape

hydraulic stress there is no change in volume

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25.

The Young's modulus of the material of a wire is 2 × 10^{10} Nm^{-2}. If the elongation strain is 1 %, then the energy stored in the wire per unit volume in Jm^{-3} is

10

^{6}10

^{8}2 × 10

^{6}2 × 10

^{8}

26.

If the volume of a block of aluminium is decreased by 1%, the pressure (stress) on its surface is increased by (Bulk modulus of Al = 7.5 10^{10} Nm^{-2})

7.5 × 10

^{10}Nm^{-2}7.5 × 10

^{8}Nm^{-2}7.5 × 10

^{6}Nm^{-2}7.5 × 10

^{4}Nm^{-2}

27.

The length of a rubber cord is 11 metre when the tension is 4 N and l_{2} metre when the tension is 6 N. The length when the tension is 9 N, is

(2.5 l

_{2}− 1.5 l_{1}) m(6 l

_{2}− 1.5 l_{1}) m(3 l

_{2}− 2 l_{1}) m(3.5 l

_{2}− 2.5 l_{1}) m

28.

A wire of natural length l, Young's modulus Y and area of cross-section A is extended by x. Then the energy stored in the wire is given by

$\frac{1}{2}\frac{\mathrm{YA}}{\mathrm{l}}{\mathrm{x}}^{2}$

$\frac{1}{3}\frac{\mathrm{YA}}{\mathrm{l}}{\mathrm{x}}^{2}$

$\frac{1}{2}\frac{\mathrm{Yl}}{\mathrm{A}}{\mathrm{x}}^{2}$

$\frac{1}{2}\frac{\mathrm{YA}}{{\mathrm{l}}^{2}}{\mathrm{x}}^{2}$

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29.

A piece of solid weighs 120 g in air, 80 g in water and 60 g in a liquid. The relative density of the solid and that of the liquid are respectively

3, 2

$2,\frac{3}{4}$

$3,\frac{3}{2}$

4, 3

30.

A work of 2 x 10^{-2} J is done on a wire of length 50 cm and area of cross-section 0.5 mm^{2}. If the Young's modulus of the matenal of the wire is 2 × 10^{10} Nm^{-2}, then the wire must be

elongated to 50.1414 cm

contracted by 2.0 mm

stretched by 0.707 mm

of length changed to 49.293 cm

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