e 10 8 101


"lb'' is short for pounds (American use instead of kilograms).
(a) The force of static friction can be as large as f\leq\mu_{s}N=(0.60)(12lb)=7.2lb.
That is enough to hold the block up with no problem.
(b) The force of static friction is just large enough to hold up the
block: f=5.0lb. The magnitude of the force of the wall on the block
is F=\sqrt{(5.0)^{2}+(12.0)^{2}}lb=13lb.