Basic important concepts on Newton’s Laws which you have to understand.
a) On a rough floor, when the applied force on a moving object is removed, the resultant force acting on object is backwards (frictional force). This resultant force causes the object to decelerate. (Newton’s 2nd Law)
A good example is that of a wakeboarder. When the tension in cable is equal to the opposing force, the wakeboarder moves at constant speed, balanced forces, net force is 0N. But the moment he releases the cable, the only force acting is the opposing force. The resultant force backwards (opposing force) causes him to slow down (decelerate). Hence resultant force backwards does not mean the wakeboarder is moving backwards.
b) On a frictionless floor, when the applied force on a moving object is removed, the resultant force acting on object is 0N, and the object will move with a constant speed in a straight line. (Newton’s 1st law)
View the video tutorial to understand the 2 concepts.