Answer:
(b) Net force causes change in motion.
Explanation:
There can be a motion even if there is no net force acting on an object.
It can be justified by giving an example:- when object is moving at constant speed then it has no net force and still is in motion.
If there is a net force acting, then the object will accelerate and this will cause change in motion.
The change in motion can be change in direction of motion, change in speed of motion.
For example when an object is moving in east direction if someone accelerate it this will result in change in motion or change in speed and after some time the net force is applies in the north direction then the object will move in the north direction which proves that the net force also causes change in direction.
