Question

A force is required to keep a body in uniform motion in a straight line . comment.

Answer 1

the object will slow down due to friction if a cons. force cancelling outthe frictional retarding force the cons.is moving body.

Answer 2

Using newtons first law : An object continues to be in its state of rest uniform motion until and unless and external unbalanced force is applied on it.
No need of mentioning friction here..