Q3. A given object takes n times the time to slide down $45 ^ { \circ }$ rough inclined plane as it takes the time to slide down an identical perfectly smooth $45 ^ { \circ }$ inclined plane. The coefficient of kinetic friction between the object and the surface of inclined plane is :\\
(1) $\sqrt { 1 - \frac { 1 } { n ^ { 2 } } }$\\
(2) $1 - n ^ { 2 }$\\
(3) $1 - \frac { 1 } { n ^ { 2 } }$\\
(4) $\sqrt { 1 - n ^ { 2 } }$