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The horizontal force $P=77N$ is applied to the upper block with the system initially stationary. The block masses are $m_A=16kg$ and $m_B=7kg.$ Determine the magnitudes of the frictions forces $F_1($between block A and the ground$)$ and $F_2($between blocks A and $B)$ for the following conditions on the coefficients of static friction: $($a$){}_1=0\mathrm{.}40,{}_2=0\mathrm{.}60$ and $($b$){}_1=0\mathrm{.}28,{}_2=0\mathrm{.}86.$ Assume that the coefficients of kinetic friction are $70$ percent of the static values.

Answers:

$($a$)F_1=N,F_2=$ N

$($b$)F_1=N,F_2=$ N