A heavy rod AB is suspended from a point O by two strings OA and OB .

[Suvadip]

A heavy rod AB is suspended from a point O by two strings OA and OB . Show that the plane OAB is vertical.

How to do this? Please help me.

 

[radou]

Well, if nothing holds the rod AB except the strings, then, in order for it to be in equilibrium, it must hang. The rest is just vector algebra (3 coplanar vectors). The forces in the string together with the weight of the rod must cancel out.