A cable spool of mass M, radius R and moment of inertia I = βMR2 around an
axis through its center of mass is wrapped around its outer disk with fishing
line and set on a rough rope as shown. The fishing line is then pulled with a
force of magnitude F to the right as shown so that it rolls down the rope on the
spool at radius r to the right without slipping.
What is the direction of static friction as it rolls?