Answer
(a) see attached free body diagram
The normal force of crate A on crate B, and the normal force of crate B on crate A, make an action-reaction pair of forces.
(b) Even if the applied force $F$ is very small, the two crates will accelerate because the surface is frictionless. There will be a net horizontal force to the right.
$F = (m_A+m_B)a$
$a = \frac{m_A+m_B}{F}$
Work Step by Step
(a) see attached free body diagram
The normal force of block A on block B, and the normal force of block B on block A, make an action-reaction pair of forces.
(b) Even if the applied force $F$ is very small, the two blocks will accelerate because the surface is frictionless. There will be a net horizontal force to the right.
$F = (m_A+m_B)a$
$a = \frac{m_A+m_B}{F}$
