The force required to keep an object at a constant velocity is-

Correct answers: (a) Net force or (e) None of the above

Explanation

By Newton's first law, a body moving at constant velocity keeps moving unless an unbalanced force acts. So no extra force is needed: all the forces on it must balance, and the net force is zero.

For example, a car at steady speed has its engine's push exactly balanced by friction and air resistance.

At constant velocity no unbalanced force is needed: the net force is zero. The key reads (a) as 'zero net force'; (e) is accepted too.