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Mechanical Properties of Solids Test - 17

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Mechanical Properties of Solids Test - 17
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  • Question 1
    1 / -0
    Consider the following two statements A and B and identify the correct answer.
    A) When the length of a wire is doubled, the Young's modulus of the wire is also doubled
    B) For elastic bodies Poisson's ratio is + Ve and for inelastic bodies Poissons ratio is -Ve
    Solution
    1/ Young's modulis is property of a metal independent of its dimensions
    2/Definition of Poisson's ratio 
    Poisson's ratio is the ratio of transverse contraction strain to longitudinal extension strain in the direction of stretching force. Tensile deformation is considered positive and compressive deformation is considered negative. The definition of Poisson's ratio contains a minus sign so that normal materials have a positive ratio.Virtually all common materials, such as the blue rubber band on the right, become narrower in cross section when they are stretched. 
  • Question 2
    1 / -0
    The poisson's ratio cannot have the value
    Solution
    The Poisson's ratio of a stable, isotropic, linear elastic material will be greater than −1.0 or less than 0.5 because of the requirement for Young's modulus, the shear modulus and bulk modulus to have positive values. Most materials have Poisson's ratio values ranging between 0.0 and 0.5.
  • Question 3
    1 / -0
    Consider the following two statements A and B and identify the correct answer.
    A) The bulk modulus for an incompressible liquid is infinite.
    B) Young's modulus increases with raise of temperature.
    Solution
    For an incompressible fluid volume change is zero. So as in expression of bulk modulus change in volume comes in denominator so the value of bulk modulus for incompressible fluid is infinity. Young's modulus decreases with increase in temperature.

  • Question 4
    1 / -0
    Consider the following two statements A and B and identify the correct answer.
    A) We cannot define Young's modulus and rigidity modulus for liquids and gases.
    B) The theoretical limits of Poisson's ratio are 1 to 0.5
    Solution
    The reciprocal of the bulk modulus is called the compressibility of the substance. The amount of compression of solids and liquids is seen to be very small.Thus youngs modulus is not defined for liquids and gases
    and 
    Theoretical limits of = 1 to 0.5. 
  • Question 5
    1 / -0
    Consider the statements A and B, identify the correct answer given below :
    (A) : If the volume of a body remains unchanged when subjected to tensile strain, the value of poisson's ratio is 1/2.
    (B) : Phosper bronze has low Young's modulus and high rigidity modulus. 
    Solution
    Experimental value of poisson's ratio is always between $$0$$ to $$1/2$$ .
    As Phosper bronze is solid so, value of young's modulus is also high.
  • Question 6
    1 / -0
    Strain energy per unit volume in a stretched string is
    Solution
    strain energy$$=\dfrac{1}{2}\times stress\times strain$$
    Work done by a force on a wire
    W $$=\dfrac{Ay(\Delta L)^{2}}{2L}$$
    $$=\dfrac{1}{2}(\dfrac{yA}{}\dfrac{\Delta L}{L})\Delta L$$
    $$=\dfrac{1}{2}(y\dfrac{\Delta L}{L})(\dfrac{\Delta L}{L})(AL)$$
    $$=\dfrac{1}{2}(stress)(strain)(volume)$$
    (Work)/(volume)$$ =\dfrac{1}{2}(stress)(strain)$$
    Option A
  • Question 7
    1 / -0
    Possible value of Poisson's ratio is
    Solution
    The Poisson's ratio of a stable, isotropic, linear elastic material cannot be less than $$1.0$$ nor greater than $$0.5$$. So only possible value among the options is $$0.4.$$
  • Question 8
    1 / -0
    Assertion (A) : Lead is more elastic than rubber.
    Reason (R) : If the same load is attached to lead and rubber wires of the same cross-sectional area, the strain of lead is very much less than that of rubber.
    Solution
    More elastic the material higher the Young's Modulus.
    Young's Modulus of rubber is 0.01-0.1 Gpa whereas for Lead it is 16 Gpa.

    Also, $$Y = (F/A)/l/L$$

    F - Applied Force
    A - Cross Section Area
    l - Elongation/Decrease in Length
    L - Actual Length
    Therefore $$l/L = F/AY$$
    for F,A same
    $$l/L$$ is inversely proportional to $$Y$$
    So, higher the Young's Modulus, lesser is the strain.
  • Question 9
    1 / -0
    Consider the following two statements A and B and identify the correct answer .
    A) A metal wire held vertically is longer than when it placed on a horizontal table.
    B) Due to its own weight, some elongation is produced when it is held vertically.
    Solution
    When metal wire is held vertically then due to gravity (it's own weight) a froce acts in downward direction which makes the wire slightly longer. On the other hand when wire is kept horizontally then it might appear slightly thick but not longer. 
  • Question 10
    1 / -0
    The Poisson's ratio $$\sigma$$ should satisfy the relation :
    Solution
    Poisson's ratio is the ratio of transverse contradiction strain to longitudinal extension strain in the direction of stretching force.
    The Poisson's ratio $$\sigma$$ should satisfy the relation,
    $$-1<\sigma <0.5$$
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