A hollow cylinder of radius `R` rotates about its axis which is vertical. A block remains in contact with the inner wall if the frequency of rotation is `f` hertz, but falls at lower frequaencies. The coefficient of friction between the block and the cylinder is

Options

A. `(g)/(2pi^(2)f^(2)R)`
B. `(g)/(4pi^(2)f^(2)R)`
C. `(g)/(pi^(2)R)`
D. `(2g)/(pi^(2)f^(2)R)`

Answer

B

Explanation

`N=momega^(2)R`
`f=muN`
`f=muN=mg`
`mumomega^(2)R=mg`
`mu=(g)/(omega^(2)R)=(g)/(4pi^(2)f^(2)R)`