A particle moves along a rough plane inclined at 30? to the horizontal. The co-efficient of friction between the particle and the plane is 0.1. Its initial velocity is 15 m/sec. The ratio of the velocity of the particle when it move down the plane to that when it move up the plane would be in the regions a.8 ? 10 b.5 ? 7 c.2 ? 3 d.4 ? 6 e.10 ? 13