A spool of thread, free to unwind, is on a horizontal surface (with friction) and pulled directly upward (+y) at all times. The spool rolls without slipping on the floor. The spool has a mass M, moment of inertia I, and a radius of R. Assume the string is wrapped around the spool at a radius r (where r < R). spool rolling on the floor

Which equation below is a correct expression of Newton’s Second Law ( ΣF=ma ) in the x (horizontal) -direction for this situation. Assume all the forces below are magnitudes and that to the right is considered the positive direction.

a. F_T - Ff= Max
b. F_T+Ff= Max
c. Ff= Max