CBSE Class 11 Elasticity Worksheet A

Question. When a weight of 10 kg is suspended from a copper wire of length 3 metres and diameter 0.4 mm, its length increases by 2.4 cm. If the diameter of the wire is doubled, then the extension in its length will be:
a. 9.6 cm
b. 4.8 cm
c. 1.2 cm
d. 0.6 cm
Answer : D

Question. The extension of a wire by the application of load is 3 mm. The extension in a wire of the same material and length but half the radius by the same load is:
a. 12 mm
b. 0.75 mm
c. 15 mm
d. 6 mm
Answer : A

Question. A force F is applied on the wire of radius r and length L and change in the length of wire is l. If the same force F is applied on the wire of the same material and radius 2r and length 2L, Then the change in length of the other wire is:
a. l
b. 2l
c. l/2
d. 4l
Answer : C

Question. Two similar wires under the same load yield elongation of 0.1 mm and 0.05 mm respectively. If the area of crosssection of the first wire is 4mm² then the area of cross section of the second wire is:
a. 6 mm²
b. 8 mm²
c. 10 mm²
d. 12 mm²
Answer : B

Question. When a uniform wire of radius r is stretched by a 2kg weight, the increase in its length is 2.00 mm. If the radius of the wire is r/2 and other conditions remain the same, the increase in its length is:
a. 2.00 mm
b. 4.00 mm
c. 6.00 mm
d. 8.00 mm
Answer : D

Question. A wire of length L and radius r is rigidly fixed at one end. On stretching the other end of the wire with a force F, the increase in its length is l. If another wire of same material but of length 2L and radius 2r is stretched with a force of 2F, the increase in its length will be:
a. l
b. 2 l
c. l/2
d. l/4
Answer : A

Question. Two wires A and B are of same materials. Their lengths are in the ratio 1 : 2 and diameters are in the ratio 2 : 1 when stretched by force FA and FB respectively they get equal increase in their lengths. Then the ratio FA/FB should be:
a. 1 : 2
b. 1 : 1
c. 2 : 1
d. 8 : 1
Answer : D

Question. A uniform plank of Young’s modulus Y is moved over a smooth horizontal surface by a constant horizontal force F. The area of cross-section of the plank is A. the compressive strain on the plank in the direction of the
a. F/AY
b. 2F/AY
c. 1/2(F/AY)
d. 3F/AY
Answer : A

Question. A 5 m long aluminum wire (Y = 7×10¹⁰ N /m² ) of diameter 3 mm supports a 40 kg mass. In order to have the same elongation in a copper wire (Y =12×10¹⁰ N /m² ) of the same length under the same weight, the diameter should now be, in mm
a. 1.75
b. 2.0
c. 2.3
d. 5.0
Answer : C

Question. The dimensions of four wires of the same material are given below. In which wire the increase in length will be maximum when the same tension is applied:
a. Length 100 cm, diameter 1 mm
b. Length 200 cm, diameter 2 mm
c. Length 300 cm, diameter 3 mm
d. Length 50 cm, diameter 0.5 mm
Answer : D

Assertion and Reason Problems

Note: Read the Assertion (A) and Reason (R) carefully to mark the correct option out of the options given below:
a. If both assertion and reason are true and the reason is the correct explanation of the assertion.
b. If both assertion and reason are true but reason is not the correct explanation of the assertion.
c. If assertion is true but reason is false.
d. If the assertion and reason both are false.
e. If assertion is false but reason is true.

Question. Assertion: Young’s modulus for perfectly plastic body is zero.
Reason: For a perfectly plastic body, restoring force is zero
Answer : A

Question. Assertion: Bulk modulus of elasticity (b) represents in compressibility of the material.
Reason: Bulk modulus of elasticity is proportional to change in pressure.
Answer : A

Question. Assertion: Steel is more elastic than rubber.
Reason: Under given deforming force. Steel is deformed less than rubber.
Answer : A

Question. Assertion: Two identical solid balls, one of ivory and the other of wet-clay are dropped from the same height on the floor. Both the balls will rise to same height after bouncing.
Reason: Ivory and wet-clay have same elasticity.
Answer : D

Question. Assertion: Two identical uniform elastic rods are lying horizontally on smooth horizontal surface under the action of forces as shown in figure. The elongation in two rods will be same.

Reason: For a uniform elastic rod, the elongation is depending on a net force acting on the rod and is independent of point of application of force.
Answer : E

Question. Assertion: The bridges are declared unsafe after a long use.
Reason: Elastic strength of bridges decreases with time.
Answer : A

Question. Assertion: The stretching of a coil is determined by its shear modulus.
Reason: Shear modulus change only shape of a body keeping its dimensions unchanged.
Answer : A

Question. Assertion: Spring balances show correct readings even after they had been used for a long time interval.
Reason: On using for long time, spring balances losses its elastic strength.
Answer : E

Question. Assertion: Steel is more elastic than rubber.
Reason: Under given deforming force, steel is deformed less than rubber.
Answer : A

Question. Assertion: Glassy solids have sharp melting point.
Reason: The bonds between the atoms of glassy solids get broken at the same temperature.
Answer : D

Question. Assertion: Sterss is the internal force per unit area of a body.
Reason: Rubber is less elastic than steel.
Answer : B

Question. Assertion: Identical springs of steel and copper are equally stretched. More work will be done on the steel spring.
Reason: Steel is more elastic than copper
Answer : A

Integer

Question. The length of a wire increases by 8 mm, when a weight of 5 kg is hung. If the conditions are the same, but the radius of the wire is doubles, what will be the increase in length in mm.
Answer : 2

Question. A lift is tied with thick iron wires and its mass is 1000 kg. If the maximum acceleration of lift is 1.2 ms^–2 and maximum safe stress is 8 2 1.4 10 Nm , × − find the minimum diameter of the wire in cm, 2 g = 9.8m/ s.
Answer : 1

Question. When equal volume of two metal are mixed together, the specific gravity of alloy is 4. When equal masses of the same two metals are mixed together, the specific gravity of the alloy is 3. Calculate the specific gravity of each metal.
Answer : 2, 6

Question. A wire is loaded by 6 kg at its one end, the increase in length is 12 mm. If the radius of the wire is doubled and all other magnitudes are unchanged, then increase in length will be
Answer : 3

Question. A wire extends by 1 mm when a force is applied. Double the force is applied to another wire of same material and length but half the radius of cross-section. The elongation of the wire in mm will be
Answer : 8

Question. One end of a horizontal thick copper wire of length 2L and radius 2R is welded to an end of another horizontal thin copper wire of length L and radius R. When the arrangement is stretched by applying forces at two ends, the ratio of the elongation in the thin wire to that in the thick wire is:
Answer : 2

Question. When a certain weight is suspended from a long uniform wire, its length increases by one cm. If the same weight is suspended from another wire of the same material and length but having a diameter half of the first one then the increase in length will be:
Answer : 4

Question. Young's modulus of rubber is 4 2 10 N / m and area of cross-section is 2 cm². If force of 5 2 × 10 dynes is applied along its length, then its initial length l becomes:

Answer : 2

Elasticity MCQ Questions with Answers Class 11 Physics

1. The stretching of a coil spring is determined by its shear modulus. Why?

2. The spherical ball contracts in volume by 0.1% when subjected to a uniform normal pressure of 100 atmosphere calculate the bulk modulus of material of ball?

3. In the following stress – strain curve, which has:-

1) Greater young’s Modulus 2) More Ductility 3) More Tensile strength.

4. A cube is subject to a pressure of 5X10⁵ N|m². Each side of cube is shortened by 1% find: - 1) the volumetric strain 2) the bulk modulus of elasticity of cube.

5. If the potential energy is minimum at r = r₀= 0.74A⁰, is the force attractive or repulsive at r = 0.5A⁰; 1.9A⁰ and α?

6. A hollow shaft is found to be stronger than a solid shaft made of same equal material? Why?

7. Calculate the work done when a wire of length l and area of cross – section A is made of material of young’s Modulus Y is stretched by an amount x?

8. Water is more elastic than air. Why?

9. Explain :-

1) Elastic Body 2) Plastic Body 3) Elasticity.

10. The length of a metal is l1, when the tension in it is T₁ and is l₂ when tension is l₂. Find the original length of wire?

Click on link below to download CBSE Class 11 Elasticity Worksheet A.