A wire of cross-section \(A_{1}\) and length \(l_1\) breaks when it is under tension \(T_{1};\) a second wire made of the same material but of cross-section \(A_{2}\) and length \(l_2\) breaks under tension \(T_{2}.\) A third wire of the same material having cross-section \(A,\) length \(l\) breaks under tension \(\dfrac{T_1+T_2}{2}.\) Then:

1. \(A=\dfrac{A_1+A_2}{2},~l=\dfrac{l_1+l_2}{2}\)
2. \(l=\dfrac{l_1+l_2}{2}\)
3. \(A=\dfrac{A_1+A_2}{2}\)
4. \(A=\dfrac{A_1T_1+A_2T_2}{2(T_1+T_2)},~l=\dfrac{l_1T_1+l_2T_2}{2(T_1+T_2)}\)
Subtopic:  Young's modulus |
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Two wires of identical dimensions but of different materials having Young's moduli \(Y_1, Y_2\) are joined end to end. When the first wire is under a tension \(T,\) it elongates by \(x_1\) while the second wire elongates by \(x_2\) under the same tension \(T.\) The elongation of the composite wire when it is under tension \(T\) is:

1. \(x_1+x_2\) 2. \(\dfrac{Y_1x_1+Y_2x_2}{Y_1+Y_2}\)
3. \(\dfrac{x_1+x_2}{2}\) 4. \(\dfrac{Y_1x_2+Y_2x_1}{Y_1+Y_2}\)
Subtopic:  Young's modulus |
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Two wires \((A, B)\) of identical lengths have breaking stresses in the ratio \(1:2,\) while their cross-sectional areas are the same. When a block of mass \(M\) is placed on the horizontal light rod, it is observed that wire \(A\) breaks if \(M\) is placed slightly to the left, while \(B\) breaks if \(M\) is placed slightly to right.

Then, \(\dfrac{x_1}{x_2}=\)
1. \(\dfrac12\) 2. \(\dfrac14\)
3. \(\dfrac21\) 4. \(\dfrac41\)
Subtopic:  Stress - Strain |
 67%
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A uniform rod of mass \(m,\) having cross-section \(A\) is pushed along its length \((L)\) by means of a force of magnitude, \(F.\) There is no friction anywhere. Ignore the weight of the rod. The longitudinal stress in the rod, at a distance \(\dfrac{L}{3}\) from the left end, is:
           
1. tensile, \(\dfrac{F}{3A}\)
2. compressive, \(\dfrac{F}{3A}\)
3. tensile, \(\dfrac{2F}{3A}\)
4. compressive, \(\dfrac{2F}{3A}\)
Subtopic:  Stress - Strain |
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A simple pendulum is made with a thin wire (length: \(l,\) area: \(A,\) Young's modulus: \(Y\)) attached to a heavy bob of mass \(M.\) The pendulum is released from the rest with the bob at the same level as the point of suspension and swings down in a circular arc. The elongation in the wire when the bob reaches the lowest point is: 
1. \(\dfrac{3 M g l}{A Y}\) 2. \(\dfrac{2 M g l}{A Y}\)
3. \(\dfrac{3 M g l}{2 A Y}\) 4. \(\dfrac{M g l}{A Y}\)
Subtopic:  Hooke's Law |
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A cube made of a homogeneous, isotropic elastic solid is acted upon by forces of equal magnitude acting perpendicular to its opposite faces as shown. Forces are applied uniformly over the area of each face. The stress at the centre of the cube is:
               

1. tensile
2. compressive
3. shear
4. zero
Subtopic:  Stress - Strain |
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An extremely long solid rod of length \(L\) starts falling longitudinally towards a large point mass \(M,\) the near end of the rod being at a distance \(L\) from the mass \(M.\) The rod experiences:
1. no stress. 2. compressive stress.
3. tensile stress. 4. shear stress.
Subtopic:  Stress - Strain |
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A large cylindrical piece of a dense solid elastic metal stands on its end as shown in the figure. The metal is uniform and isotropic. The stress in the material as a function of height is shown correctly by:
   
1. 2.
3. 4.
Subtopic:  Stress - Strain Curve |
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The block, shown in the figure, is suspended as shown from two identical steel wires. The extension in the wires due to the tension is \(\Delta l_1.\) If the block is suspended by one of the wires the extension in it is \(\Delta l_2.\) Then \(\dfrac{\Delta l_1}{\Delta l_2}\) equals:
                
1. \(1\) 2. \(2\)
3. \(\sqrt 2\) 4. \(\dfrac12\)
Subtopic:  Young's modulus |
 66%
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A uniform rod \(AB\) is rotated at a constant angular speed about its end \(A,\) the rotation axis being perpendicular to \(AB.\) During rotation, stresses are set up in the rod. Let the stress at \(A\) be \(\sigma_A\) and that at the centre \(C\) be \(\sigma_C.\) Then:
                   

1. \(\sigma_A=\sigma_C\)
2. \(\sigma_A=2\sigma_C\)
3. \(\sigma_C=2\sigma_A\)
4. \(\sigma_C=\dfrac34\sigma_A\)
Subtopic:  Stress - Strain |
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