Suppose, no net force is acting on an object. Which of the following situations are possible?
Object remains at rest if at rest.
Possible. As per Newton's first law, if no net force acts on an object, it will either remain at rest or move with a constant velocity. Thus, an object at rest remains at rest.
Object keeps moving with a constant velocity if already moving.
Possible. An object already moving will continue moving with a constant velocity because it cannot change its velocity.
Object is moving with a constant acceleration.
Not possible. When the net force is zero, the object cannot change its velocity, meaning its acceleration is zero. Therefore, it cannot move with a constant acceleration.
Explanation
The textbook states that when no net force is acting on an object, there are only two possibilities: either the object is at rest or it is moving with a constant velocity. If the net force is zero, the body cannot begin to move or change its velocity, which means its acceleration must be zero. Therefore, situations (i) and (ii) are possible, but situation (iii) is impossible.