F=ma and for constant velocity acceleration is zero so force should be
But how's that even possible? Cause of motion is force and how can
body be moving if no net force is acting on it?
Example 1: a body moving on a frictionless surface at constant velocity has no net force acting upon it. A force would be required to start it moving, but no force is necessary to keep it moving.
Example 2: A body moving at constant velocity on a surface with friction where the force pushing the body exactly equals the opposing kinetic friction force. There is no net force, yet the body is moving. Once again a net force would be required initially to overcome static friction, but once the body starts moving all that is needed is a force equal to the opposing kinetic friction force to keep it moving.
Hope this helps.