A long steel rod of uniform cross sectional area is suspended from one end. If x be the elongation of lower half of the rod, the elongation of upper half is

Let m be the mass of the rod, l be its length and S be its cross sectional area and Y be the Young's modulus of steel,  then elongation of lower half BC, x=(mg2)l4SY=mgl8SYElongation of upper half AC, y=(mg2)l4S.Y+(mg2)l2SY⇒y=38mglSY⇒y=3x