Question

If the $10\text{kg}$ and $20\text{kg}$ bodies are considered to be system $1$ and $30\text{kg}$ body is considered as system $2$. The number of forces that would appear to be acting as an external force for system 1 is

Answer 1

Drawing FBD of system 1

The tension in the rope between 10 kg and 20 kg is internal to the system and therefore not shown in FBD.