An object is placed on the surface of smooth inclined plane of inclination `theta`. It takes time t to reach the bottom. If the same object is allowed to slide down the rough inclined plane of the same inclination, the time to reach the bottom is increased n times where n > 1. The coefficient of friction for the plane is
`mu` = tan `theta` `[1-1/n^2]`
`mu` = cot `theta` `[1 - 1/n^2]`
`mu` = tan `` ` `` ````theta` ` ``[1- 1/n^2]^(1/2)`
`mu` = cot `theta` `[1 - 1/n^2]^(1/2)`