In the figure below, a uniform plank, with a length L of 6.20 m and a weight of 460 N, rests on the ground and against a frictionless roller at the top of a wall of height h = 3.10 m. The plank remains in equilibrium for any value of e z 70° but slips if e < 70°. Find the coefficient of static friction between the plank and the ground. Roller

In the figure below, a uniform plank, with a length L of 6.20 m and a weight of 460 N, rests on the ground and against a frictionless roller at the top of a wall of height h = 3.10 m. The plank remains in equilibrium for any value of e z 70° but slips if e < 70°. Find the coefficient of static friction between the plank and the ground. Roller