In a ring ABCD of radius r, the lower half ABC has mass m and the upper half ADC has mass `2m`. In both parts, the masses are distributed evenly. The ring is initially at rest on a horizontal surface, as shown. O is the centre of the ring.


The ring is now folded along the diameter AC, such that the plane of the section ABC is normal to the plane of the section ADC. (The angle BOD `= 90^(@)`). It is then placed on a thin, fixed horizontal wire, ie.e, the diameter AC lies along the wire. The angle made by DO with the vertical will now be

Options

A. `tan^(-1)(2//3)`
B. `tan^(-1) (1//2)`
C. `30^(@)`
D. `60^(@)`

Answer

B