b
(b) Limiting friction ${F_l} = {\mu _s}R = 0.5 \times (5) = 2.5\;N$
Since downward force is less than limiting friction therefore block is at rest so the static force of friction will work on it.
${F_s}$ $=$ downward force $=$ Weight
$ = 0.1 \times 9.8 = 0.98\,N$
