Blocks $A,B,$ and $C$ in $($Figure $1)$ have weights of $60N,30N,$ and $20N,$ respectively.

Figure

$1$ of $1$

Part A

Determine the smallest horizontal force $P$ that will cause impending motion. The coefficient of static friction between A and $B$ is ${}_s=0\mathrm{.}3,$ between $B$ and $C,{}_s^{\text{'}}=0\mathrm{.}4,$ and between block $C$ and the ground, ${}_s^{\text{'}\text{'}}=0\mathrm{.}35.$