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NCERT Solutions for class 11 Physics | Chapter 9 - Mechanical Properties of Solids

(1) The reason for the change in shape of a regular body is
[A] volume stress
[B] shearing strain
[C] longitudinal strain
[D] metallic strain
Answer: volume stress
(2) After terminal velocity is reached, the acceleration of a body falling through a fluid is
[A] zero
[B] equal to g
[C] less than g
[D] greater than g
Answer: zero

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(3) Which of the following statements is/are wrong?

I. Hollow shaft is much stronger than a solid rod of same length and same mass.

II. Reciprocal of bulk modulus of elasticity is called compressibility.

III. It is difficult to twist a long rod as compared to small rod.

[A] III only
[B] I only
[C] II and III
[D] I and II
Answer: III only
(4) Terminal velocity of ball depends on
[A] density difference of liquid and ball
[B] density of ball only
[C] density of liquid only
[D] area of the ball
Answer: density difference of liquid and ball
(5) If a soap bubble formed at the end of the tube is blown very slowly, then the graph between excess pressure inside the bubble with time will be a
[A] parabolic curve sloping down
[B] parabolic curve sloping up
[C] straight line sloping down
[D] straight line sloping up
Answer: parabolic curve sloping down
(6) A wire suspended vertically from one of its ends is stretched by attaching a weight of 100N to its lower end. What is the elastic potential energy stored in the wire, if the weight stretches the wire by 1.5 mm?
[A] 5 × 10-2 J
[B] 10-3 J
[C] 2.5 × 10-3 J
[D] 7.5 × 10-2 J
Answer: 7.5 × 10-2 J
(7) Shearing strain is given by
[A] Deforming force
[B] Shape of shear
[C] Angle of shear
[D] Change in volume of the body
Answer: Angle of shear
(8) If a wire having initial diameter of 2 mm produced the longitudinal strain of 0.1%, then the final diameter of wire will be (s = 0.5)
[A] 2.002 mm
[B] 1.998 mm
[C] 1.999 mm
[D] 2.001 mm
Answer: 1.999 mm
(9) Under the action of load F1, the length of a string is L1 and that under F2, is L2. the original length of the wire is
[A] [L1F1 - L2F2] / [F1 + F2]
[B] [L1F2 - L2F1] / [F1 - F2]
[C] [L1F2 - L2F1] / [F2 - F1]
[D] [L1F2 - L2F1] / [F1 + F2]
Answer: [L1F2 - L2F1] / [F2 - F1]
(10) A body of mass 1 kg is attached to one end of a wire and rotated in horizontal circle of diameter 40 cm with a constant speed of 2 m/s. what is the area of cross-section of the wire if the stress developed in the wire is 5 × 106 N/m2 ?
[A] 2 mm2
[B] 3 mm2
[C] 4 mm2
[D] 5 mm2
Answer: 4 mm2
(11) The compressibility of water is 4 × 10-5 per unit atmospheric pressure. 100cc of water is subjected to a change of pressure of 100 atmospheres. The change in the volume will be
[A] 4 × 10-5 cc
[B] 4 × 10-2 cc
[C] 4 × 10-4 cc
[D] 4 ?×10-1 cc
Answer: 4 ?×10-1 cc
(12) The radii of two wires of a same material are in ratio 2:1. if the wires are stretched by equal forces, the stress produced in them will be
[A] 2:1
[B] 4:1
[C] 1:4
[D] 1:2
Answer: 1:4
(13) The ratio of the change in dimension at right angles to the applied force to the initial dimension is known as
[A] Youngs modulus
[B] Poissons ratio
[C] Lateral strain
[D] Shearing strain
Answer: Lateral strain
(14) The Youngs modulus for a plastic body is
[A] One
[B] Zero
[C] Infinity
[D] Less then one
Answer: Zero
(15) If by applying a force, the shape of a body is changed, then the corresponding stress is known as
[A] Tensile stress
[B] Bulk stress
[C] Shearing stress
[D] Compressive stress
Answer: Shearing stress
(16) The force constant of a wire is K and that of another wire of the same material is 2K. when both the wires are stretched by the same force, then the work done is
[A] W2 = W1
[B] W2 = 0.5 W1
[C] W2 = 2W1
[D] W2 = 2W12
Answer: W2 = 0.5 W1
(17) If a material is heated and annealed, then its elasticity is
[A] Increased
[B] Decreased
[C] Not change
[D] Becomes zero
Answer: Decreased
(18) Four steel wires of the following dimensions are stretched with the same force. Which one of them will have the largest extension?
[A] L1 = 50 cm, r1 = 0.5 mm
[B] L2 = 100 cm, r2 = 1 mm
[C] L3 = 200 cm, r3 = 2 mm
[D] L4 = 300 cm, r4 = 3 mm
Answer: L1 = 50 cm, r1 = 0.5 mm
(19) The Youngs modulus for a plastic body is
[A] One
[B] Zero
[C] Infinity
[D] Less then one
Answer: Zero
(20) To compress a liquid by 10% of its original volume, the pressure required is 2 105 atmosphere. The bulk modulus of liquid is
[A] 2 x105 N/m2
[B] 2x 107 N/m2
[C] 2x 104 N/m2
[D] 2 x106 N/m2
Answer: 2 x106 N/m2

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