Starting from rest, the time taken by a body sliding down on a rough inclined plane at $45^{\circ}$ with the horizontal is, twice the time taken to travel on a smooth plane of same inclination and same distance. Then the coefficient of kinetic friction is

Question

\[\begin {array} {1 1} (1)\;0.25 & \quad (2)\;0.33 \\ (3)\;0.50 & \quad (4)\;0.75 \end {array}\]