Question

How can it be said that an object in Uniform motion is in equilibrium as it is being acted upon by a net externel force in the direction of motion? To be in equilibrium all the forces acting on it should cancel each other, right?

Answer 1

Object that are moving with constant velocity are said to be in equilibrium only if it follows following conditions:
(i) the net force acting on the object is zero.i.e., $\sum _{}^{}\underset{F}{\to }=0$
(ii) if the object is in equilibrium, then the acceleration of an object can be zero. i.e., $\underset{a}{\to }=0$
Here the object is in uniform motion as the vector sum of all the forces acting on an object is zero(driving force = opposing friction force), so the object is said to be in equilibrium.