### Three Crates

Three crates with masses $m_{1}=45.2kg$,$m_{2}=22.8kg$ and $m_{3}=34.3kg$
on a horizontal frictionless surface.

a) What horizontal force F is needed to push the crates to the right,
as one unit, with an acceleration of $1.32m/s^{2}$?

b) Find the force exerted by $m_{2}$ on $m_{3}$.

c) Find the force exerted by $m_{1}$ on $m_{2}$.