NCERT Physics Class 11 Exemplar Ch 9 Mechanical Properties of Solids Part 3

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One and More Than One Answer

Q. 12 For an ideal liquid

(a) the bulk modulus is infinite.

(b) the bulk modulus is zero.

(c) the shear modulus is infinite.

(d) the shear modulus is zero.

Answer: (a), (d)

Q.13 A copper and a steel wire of the same diameter are connected end to end. A deforming force F is applied to this composite wire which causes a total elongation of 1cm. The two wires will have

(a) the same stress.

(b) different stress.

(c) the same strain.

(d) different strain.

Answer: (a), (d)

Very Short Answer

Q.14 The Young’s modulus for steel is much more than that for rubber. For the same longitudinal strain, which one will have greater tensile stress?

Answer: Steel

Q.15 Is stress a vector quantity?

Answer: No

Q.16 Identical springs of steel and copper are equally stretched. On which, more work will have to be done?

Answer: Copper

Q.17 What is the Young’s modulus for a perfect rigid body?

Answer: Infinite

Q. 18 What is the Bulk modulus for a perfect rigid body?

Answer: Infinite

Short Answer

Q.19 A wire of length L and radius r is clamped rigidly at one end. When the other end of the wire is pulled by a force f, its length increases by l. Another wire of the same material of length and radius , is pulled by a force Find the increase in length of this wire.

Answer: Let Y be the Young’s modulus of the material.

Then

Let the increase in length of the second wire be .Then

Or,

Q.20 A steel rod ) of length 1 m and area of cross-section is heated from , without being allowed to extend or bend. What is the tension produced in the rod?

Answer: Because of the increase in temperature the increase in length per

unit length of the rod is

Let the compressive tension on the rod be T and the cross sectional

area be a, then