Question

Joe and Bill are playing tug-o-war. Joe is pulling with a force of 200 N. Bill is simply hanging on, but skidding towards Joe at a constant velocity. What is the force of friction between Bill's feet and the ground?

Answer 1

Only unbalanced forces cause acceleration. Since Bill is not accelerating, the 200N force must be exactly balanced by friction. Thus the friction between Bill's feet and the ground is 200N.