Aladder of length l and mass m leans against a vertical wall, making an angle with respect to horizontal ground. a wheel mounted at the top of the ladder assures that the ladder can slide up and down the wall without friction. the ladder is however subject to a frictional force along the ground. that force can be any magnitude that is required to prevent slipping, but has a maximum magnitude ugm, where u is the coefficient of static friction. above that magnitude, the ladder will slip. under these circumstances, there is a smallest angle o at which the ladder is stable against falling to the ground. you have probably worked out this problem before using f=ma, but let's solve it here using the principle of virtual work. (a) identify the applied forces acting on the ladder. (b) identify the forces of constraint acting on the ladder. (c) describe any allowed virtual displacements of the ladder. (d) using the principle of virtual work for static equilibrium, determine the smallest angle o. at which the ladder is stable against falling.