A sled is pulled with a horizontal force of 20 N along a level trail, and the accelerati...

A sled is pulled with a horizontal force of 20 N along a level trail, and the acceleration is found to be An extra mass m = 4.5 kg is placed on the sled. If the same force is just barely able to keep the sled moving, what is the coefficient of kinetic friction between the sled and the trail?