Physics - NLM Question with Solution | TestHub

Horizontal component of the force: $40\cos 60^{\circ }=20\mathrm{N}$. Surface is frictionless, so acceleration of the system $a=\frac{20}{10}=2m/{\mathrm{s}}^2$.

Force by the 4 kg block on the 6 kg block $=$ force by the 6 kg block on the 4 kg block $=4\times 2=8\mathrm{N}$ (to the left, opposing the push).