Three identical rods each of length L and mass 2m are joined to form a U-shape as shown in figure. The distance of centre of mass of the combined system from the corner ‘O’ is

r→1=L2i^                 r→2=L2j^ r→3=Li^+L2j^       r→cm=m1r1+m2r2+m3r3m1m2m3 =2mL2i^+2mL2j^+2m(Li^+L2j^)6m =mLi^+mLj^+2mLi^+mLj^6m =l6(3i^+2j^)=136L