A block rests on a rough plane whose inclination `theta` to the horizontal can be varied. Which of the following graphs indicates how the friction force `F` between the block and the plane varies as `theta` is increased?

Options

A.
B.
C.
D.

Answer

B

Explanation

Let `alpha =` angle of repose
For `theta le alpha` Block is stationary and force of friction,
`f = mg sin theta`
or `f prop sin theta`
i.e. it is sine graph
For `theta ge alpha` Block sides downwards
`f = mu mg sin theta`
or `f prop cos theta`
i.e. it is cosine graph
the correct alternative is therefore (b).