Figure shows a block kept on a rough inclined plane. The maximum external force along the plane downwards for which the block remains at rest is 1N while the maximum external force along the incline upwards for which the block is rest is 7N. The coefficient of static friction `mu` is

Options

A. `(sqrt(3))/2`
B. `1/(sqrt(6))`
C. `sqrt(3)`
D. `4/(3sqrt(3))`

Answer

D

Explanation

When block is about to slide down
`1+mg sin theta=mu mg cos theta ......(1)`
when block is about to slide up
`mg sin theta+mu mg cos theta=7`......(2)
from (1) and (2) `mu=4/(3sqrt(3))`