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NTA Abhyas 2020
Exam
NTA Abhyas
Year
2020
Subject
Physics
Chapter
Mechanical Properties of Solids

NTA Abhyas 2020 · Physics · Mechanical Properties of Solids

Two wires of diameter 0.25 cm, one made of steel and other made of...

Two wires of diameter 0.25 cm, one made of steel and other made of brass are loaded as shown in figure. The unloaded length of steel wire is 1.5 m& and that of brass wire is 1.0 m. Young's modulus of steel is 2.0 × 10^{11}& and Young's modulus & of Brass& 0.91 × 10^{11} Pa. The elongations of steel and brass wires are respectively

Two wires of diameter 0.25 cm, one made of steel and other made of brass are loaded as shown in figure. The unloaded

Options

  1. A1.3 × 10^{-2}& m;
    1.5 × 10^{-4} m
  2. B1.5 × 10^{-4}& m;
    1.3 × 10^{-4} m
  3. C2.0 × 10^{-5}& m;
    1.8 × 10^{-3} m
  4. D1.8 × 10^{-3}& m;
    2.1 × 10^{-3} m

Correct answer

B. 1.5 × 10^{-4}& m;
1.3 × 10^{-4} m

Step-by-step solution

Given, diameter of wires (2r)=0.25 cm r=0.125 cm=1.25 × 10^{-3} m For steel wire, Load (F_{1})=(4 + 6) kgf=10 × 9.8 N=98 N Length of steel wire (l_{1})=1.5 m Young's modulus (Y_{1})=2.0 × 10^{11} Pa Young’s modulus (Y)=F1×l1A1×\Deltal1Change in length(\Deltal1)=F1×l1A1×Y1=F1×l1\pir12×Y1=98×1.53.14×(1.25×10−3)2×2.0×1011\text{Young's modulus (Y)}=\dfrac{{F}_{1} \times {l }_{1}}{{A}_{1} \times \text{\Delta} {l }_{1}} \text{Change in length} \left(\text{\Delta} {l }_{1}\right)=\dfrac{{F}_{1} \times {l }_{1}}{{A}_{1} \times {Y}_{1}} =\dfrac{{F}_{1} \times {l }_{1}}{\text{\pi} {r}_{1}^{2} \times {Y}_{1}} =\dfrac{\text{98} \times \text{1.5}}{\text{3.14} \times {\left(\text{1.25} \times {10}^{- 3}\right)}^{2} \times \text{2.0} \times {10}^{11}} =1.5 × 10^{-4} m For brass wire, Load (F_{2})=6 kgf=6 × 9.8 N=58.8 N Length of brass wire (l_{2})=1.0 m Young's modulus (Y_{2})=0.91 × 10^{11} Pa Change in length(l2)=F2×l2\pir22×Y2=58.8×1.03.14×(1.25×10−3)2×0.91×1011\text{Change in length} \left({l }_{2}\right)=\dfrac{{F}_{2} \times {l }_{2}}{\text{\pi} {r}_{2}^{2} \times {Y}_{2}} =\dfrac{\text{58.8} \times \text{1.0}}{\text{3.14} \times {\left(\text{1.25} \times {10}^{- 3}\right)}^{2} \times \text{0.91} \times {10}^{11}} =1.3 × 10^{-4} m
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