Question

Two blocks of mass $4kg$ and $2kg$ are placed side by side on a smooth horizontal surface as shown in the figure. A horizontal force of $20N$ is applied on $4kg$ block. Find the acceleration of each block.

Answer 1

Since, both the blocks will move with same acceleration (say $a$ ) in the horizontal direction.
Let us take both the blocks as a system.

Net external force on the system is $20N$ in horizontal direction.

Using $\Sigma F_x=m{a}_x$, we have:
$20=(4+2)a=6a$
or $a=\frac{10}{3}m/s^2$