: Block A$,$ B$,$ and C have weights of $A,B$ and $C$ respectively. Determine the smallest $P$ that will cause impending motion. The coefficient of static friction ${}_s$ between block A and $B=0\mathrm{.}3,$ between $B$ and $C$ is $0\mathrm{.}4$ and between $C$ and $D$ is $0\mathrm{.}35.$ Let Weight of the block $C=10N.$ Weight of block $B=15N$ and weight of block $A=30N.$