Question

A person pulls a box along the ground at a constant speed. If we say Earth and the box as our system, what can we say about the net external force on the system?

Answer 1

As per the question,

An object, which is moving under the force F with constant speed. The given force balance diagram representing the situation.

Here the weight of the object will be balanced by the normal reaction force and the applied force is balanced by the friction force, Hence the sum of the net force on the object is zero. hence it can move with the constant speed, and the sum of net external force is zero, so we can say it in equilibrium situation.