Three identical smooth cylinders each of mass $\sqrt{3} \mathrm{kg}$ are placed as shown in the figure. Find normal reaction between cylinder A and cylinder B. 

                 

 mg can be resolved into two forces of equal magnitude F inclined at an angle $60°$ with each other

$$\begin{gathered} \therefore \sqrt{F^2+F^2+2F^2\cos 60°}=\sqrt{3}g \\ 3F^2=3g^2 \\ F=g\text{ or }F=10 \mathrm{N} \end{gathered}$$

Hence, reaction of B on A=10N.