A steel wire is 4.0m long and 2mm in diameter. How much is it elongated by a suspended body of mass 20 kg? Young’s modulus for steel is 1,96,000 Mpa.

Let ΔL  be the elongation. Then by Hooke’s law, FA=YΔLL  where Y is Young’s modulus.The elongation is ΔL=1YFAL=mgLYA =(20)(9.8)(4.0)(196×109)π(0.001)2 =1.273×10−3m=1.273mm