Question $3$: Determine the angle $$ at which the force $F$ is minimum for the block shown

in Figure $2$ to be at the verge of sliding up the slope.

Question $4$: Given the same block shown in Figure $2,$ calculate the force $F$ necessary to

move the weight when $=30,{}_s=0\mathrm{.}3=23$ and $M=25kg.$

Figure $2$