A rubber rope of length 8m is hung from the ceiling of a room. What is the increase in length of rope due to its own weight? (Given : Young's modulus of elasticity of rubber =5×106N/m and density of rubber =1.5×103kg/m3. Take g=10m/s2).
A
1.5mm
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B
6mm
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C
24mm
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D
96mm
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Solution
The correct option is D96mm Y=MgA×L/2△L (Length is taken as L/2 because weight acts at C.G.) Now, M=ALρ. (For the purpose of calculation of mass, the whole of geometrical length L is to be considered) ∴Y=ALρgL2A△L or △L=ρgL22Y=1.5×103×10×8×82×5×106m =9.6×10−2m=9.6×10−2×103mm =96mm.