Halliday, Resnick & Walker — Force and Motion–I: Problem 56

In Fig. 5.34a, a constant horizontal force \(\vec{F}_a\) is applied to block \(A\), which pushes against block \(B\) with a \(20.0\text{ N}\) force directed horizontally to the right. In Fig. 5.34b, the same force \(\vec{F}_a\) is applied to block \(B\); now block \(A\) pushes on block \(B\) with a \(10.0\text{ N}\) force directed horizontally to the left. The blocks have a combined mass of \(12.0\text{ kg}\). What are the magnitudes of (a) their acceleration in Fig. 5.34a and (b) force \(\vec{F}_a\)?