A steel wire of length 15 m has density = 7.7 × 103 kg

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 Multiple Choice QuestionsMultiple Choice Questions

111.

Two wires of same material and length are stretched by the same force. Their masses are in the ratio 4 : 3. The ratio of their elongation will be

  • 16 : 9

  • 9 : 16

  • 4 : 3

  • 3 : 4


112.

A wire suspended vertically from one of its ends is stretched by attaching a weight 100 N to the lower end. The wire stretches by 1mm. The elastic energy stored in the wire is

  • 0.02 J

  • 0.05 J

  • 0.1 J

  • 0.2 J


113.

A circular metal plate of radius 5 cm rests on a layer of centre oil 2mm thick whose coefficient of viscosity is 15.5 dyne cm-2 s. The value of shearing stress when a horizontal force move the plate with a speed of 5 cm/s will be

  • 387.5 dyne cm-2

  • 328 dyne cm-2

  • 250 dyne cm-2

  • 428 dyne cm-2


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114.

A steel wire of length 15 m has density = 7.7 × 103 kg/m3 and Young's modulus = 2.2 × 1011 N/m2. It is subjected to a tension which produces an elastic strain of 1%. Its fundamental frequency of vibration must be

  • 256 Hz

  • 178 Hz

  • 170 Hz

  • 200 Hz


B.

178 Hz

Young's · modulus = stressstrain                            Y = Tπr2/ strain                   Tπr2 = Y × strainFundamental frequency, n = 12lTπr2ρ                                          =  12lY × strainρ                                          = 12 × 1.52.2 × 1011 × 0.017.7 × 103                                          = 178 Hz


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115.

A wire canbe brokenbyapplyinga load of200 N. The force required to break another wire of the same length and same material, but double in diameter, is

  •  200 N

  • 400 N

  • 600 N

  • 800 N


116.

A cube of side 40 mm has its upper face displaced by 0.1 mm by a  tangenbtial force of 8 kN. The shearing modulus of cube is

  • 2 × 109 Nm-2

  • Shearing modulus of cube       η = FlAl = 8 × 103 × 40 × 10-340 × 10-32 × 0.1 × 10-3         = 2 × 109  Nm-2 Nm-2

  • 8 × 109 Nm-2

  • 16 × 109 Nm-2


117.

A wire of length L and area of cross-section A is stretched through a distance x metre by applying a force F along length, then the work done in this process is (Y is Young's modulus of the material)

  • 12 A . L YxL xL

  • A .L YL xL

  • 2A . L YL xL

  • 3 A . L YL xL


118.

The modulus of elasticity is dimensionally equivalent to

  • strain

  • force

  • stress

  • coefficient of viscosity


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119.

Which of the following substance has the highest elasticity ?

  • Steel

  • Copper

  • Rubber

  • Sponge


120.

The Poisson's ratio of a material is 0.5. If a force is applied to a wire of this material, there is a decrease in the cross-sectional area by 4%. The percentage increase in the length is

  • 1 %

  • 2 %

  • 2.5 %

  • 4 %


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