Question

1)an object is placed on the surface of a smooth inclined plane of inclination θ.it takes time t to reach the bottom. if the same object is allowed to slide down inclined plane on inclination θ,it takes time nt to reach the bottom where n is a number greater than 1. what is coefficient?
2)The force required to just move a body up the inclined plane is doublethe force required to justprevent the body from sliding down the plane.the coefficient of friction is μ.find the inclination θ of the plane
3)a particle inside a hollow sphere of radius r, having coeffient of friction(1/√3), upto what height can particle be at rest?