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27. Why the spring is made up of steel in comparison of copper

27. Why the spring is made up of steel in comparison of copper (a) Copper is more costly than steel (b) Copper is more elastic than steel (c) Steel is more elastic than copper (d) None of the above ANSWER-C …

26.Two wires of equal lengths are made of the same material. Wire A has a diameter that is twice as that of wire B. If identical weights are suspended from the ends of these wires, the increase in length is

26.Two wires of equal lengths are made of the same material. Wire A has a diameter that is twice as that of wire B. If identical weights are suspended from the ends of these wires, the increase in length is …

25. The spring balance does not read properly after its long use, because

25. The spring balance does not read properly after its long use, because (a) The elasticity of spring increases (b) The elasticity decreases (c) Its plastic power decreases (d) Its plastic power increases EXPLANATION-B (243)

21. The Young’s modulus of a rubber string 8 cm long and density

The Young’s modulus of a rubber string 8 cm long and density 1.5 kg/m3 is 5×108 N/m2 , is suspended on the ceiling in a room. The increase in length due to its own weight will be (a) 9.6×10-5 m …

107.

The mean distance between the atoms of iron is 3×10-10 m and interatomic force constant for iron is 7 N/m. The Young’s modulus of elasticity for iron is (a) 2.33×105 N/m2 (b) 23.3×1010 …

106. 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 force is

(a) F/(AY) (b) (2F)/(AY) (c) 1/2{ F/(AY)} …

105. A pan with set of weights is attached with a light spring. When disturbed, the mass-spring system oscillates with a time period of 0.6 s. When some additional weights are added then time period is 0.7s. The extension caused by the additional weights is approximately given by

(a) 1.38 cm (b) 3.5 cm (c) 1.75 cm (d) 2.45 cm Answer-b (36)

98. The length of an elastic string is a metre when the longitudinal tension is 4 N and b metre when the longitudinal tension is 5 N. The length of the string in metre when the longitudinal tension is 9 N is

(a) a-b (b) 5b-4a (c) 2b-(1/4)a …

97. 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) 6.00mm (d) 8.00 mm Answer-d (10)

104. According to Hook’s law of elasticity, if stress is increased, the ratio of stress to strain

(a) Increases (b) Decreases (c) Becomes zero (d) Remains constant Answer-d (9)

100. Which is correct relation

(a) Y<σ (b) Y>σ (c) Y= σ (d) σ=+1 Answer-b (32)

99. Stress to strain ratio is equivalent to

(a) Modulus of elasticity (b) Poission’s Ratio (c) Reyhold number (d) Fund number Answer-a (7)

91. A load W produces an extension of 1mm in a thread of radius r. Now if the load is made 4W and radius is made 2r all other things remaining same, the extension will become

(a) 4 mm (b) 16 mm (c) 1 mm (d) 0.25 mm Answer-c (22)

92. The units of Young ‘s modulus of elasticity are

(a) Nm-1 (b) N-m (c) Nm-2 …

89. Under elastic limit the stress is

(a) Inversely, proportional to strain (b) Directly proportional to strain (c) Square root of strain (d) Independent of strain Answer-b (16)

88. The modulus of elasticity is dimensionally equivalent to

(a) Surface tension (b) Stress (c) Strain (d) None of these Answer-b (16)

87. 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 (10)

86. In solids, inter-atomic forces are

(a) Totally repulsive (b) Totally attractive (c) Combination of (a) and (b) (d) None of these Answer-c (5)

80. 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 (37)

85. An iron rod of length 2m and cross section area of , stretched by 0.5 mm, when a mass of 250 kg is hung from its lower end. Young’s modulus of the iron rod is

(a) 19.6×1010 N/m2 (b) 19.6×1015 N/m2 (c) 19.6×1018 N/m2 (d) 19.6×1020 N/m2 Answera-a (7)

84. Which of the following affects the elasticity of a substance

(a) Hammering and annealing (b) Change in temperature (c) Impurity in substance (d) All of these Answer-d (5)

83. If a spring is extended to length l, then according to Hook’s law

(a) F=kl (b) F=k/l (c) F=k 2l …

82. In which case there is maximum extension in the wire, if same force is applied on each wire

(a) L = 500 cm, d = 0.05 mm (b) L = 200 cm, d = 0.02 mm (c) L = 300 cm, d = 0.03 mm (d) L = 400 cm, d = 0.01 mm Answer-d (11)

73. A fixed volume of iron is drawn into a wire of length L. The extension x produced in this wire by a constant force F is proportional to

(a) 1/L2 (b) 1/L (c) L2 …

75. To keep constant time, watches are fitted with balance wheel made of

(a) Invar (b) Stainless steel (c) Tungsten (d) Platinum Answer-a (9)

76. A wire is stretched by 0.01 m by a certain force F. Another wire of same material whose diameter and length are double to the original wire is stretched by the same force. Then its elongation will be

(a) 0.005 m (b) 0.01 m (c) 0.02 m (d) 0.002 m Answer-a (7)

77. The possible value of Poisson’s ratio is

(a) 1 (b) 0.9 (c) 0.8 (d) 0.4 ANSWER-d (16)

70. Density of rubber is d. A thick rubber cord of length L and cross-section area A undergoes elongation under its own weight on suspending it. This elongation is proportional to

(a) dL (b) Ad/L (c) Ad/L2 …

69. Two wires ‘A’ and ‘B’ of the same material have radii in the ratio 2 : 1 and lengths in the ratio 4 : 1. The ratio of the normal forces required to produce the same change in the lengths of these two wires is

(a) 1 : 1 (b) 2 : 1 (c) 1 : 4 (d) 1 : 2 Answer-a (11)

67. 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 (18)

59. Which of the following statements is correct

(a) Hooke’s law is applicable only within elastic limit (b) The adiabatic and isothermal elastic constants of a gas are equal (c) Young’s modulus is dimensionless (d) Stress multiplied by strain is equal to the stored energy Answer-a (41)

63. A copper wire and a steel wire of the same diameter and length are connected end to end and a force is applied, which stretches their combined length by 1 cm. The two wires will have

(a) Different stresses and strains (b) The same stress and strain (c) The same strain but different stresses (d) The same stress but different strains Answer-d (11)