A 16.0 m uniform ladder weighing 520 N rests against a frictionless wall. The ladder makes a 57.0° angle with the horizontal. Suppose that an 840 N firefighter has climbed 4.20 m along the ladder from the bottom.
a. Find the horizontal and vertical forces that the ground exerts on the base of the ladder.
b. Now suppose that the ladder is just on the verge of slipping when the firefighter is 8.80 m from the bottom, what is the coefficient of static friction between ladder and ground?