A box with mass M slides down a ramp with friction coefficient u at a constant velocity. What is the acceleration of the box and the angle of the ramp?
The acceleration is 0, since the speed is constant. To find the angle you need to draw all the forces acting on the box, find the projection of all forces on the line which is parallel to the inclined plane and to equate the sum of projections directed "down" to the sum of projections directed "upwards". Express the angle of the resulting equation.