#1 A 4.0-kg block is on an incline plane of 30 degrees angle with respect to horizontal. a)What is the minimum coefficient of static friction (Us)min is need to prevent it from sliding down? b) When the surface us is 0.30 (which is less than the (Us)min, this means the block is going to slide down the incline] , to prevent the block sliding, a horizontal force F is applied to the block. Please find the magnitude of this force F. c) When a 20 N uphill force is applied to the block, the block starts to move up along the incline. Find the acceleration of the block. The coefficient of kinetic friction is 0.25