A wooden rod of a uniform cross section and of length `120 cm` is hinged at the bottom of the tank which is filled with water to a height of `40 cm`. In the equilibrium position, the rod makes an angle of `60^@` with the vertical. The centre of buoyancy is located on the rod at a distance (from the hinge) of

Options

A. `20cm`
B. `40cm`
C. `60cm`
D. `75cm`

Answer

B

Explanation

`OP` is the portion of the immersed in water.
`cos60^@=40/(OP)`
or `OP=40/(cos60^@)cm=40/(1/2)cm=80cm`
The centre of buoyant is at the centre of the immersed part of the rod. So, the required distance is `40 cm`.