Question

when is the force positive or negative or zero

Answer 1

When the force acts in the direction of motion it is positive and negative when it acts in the opposite direction of motion.
When there is no movement then there is zero force acting. The forces are balanced in this case.
Hope this will be helping you.
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Answer 2

forced act all directions two force act between them equally opposite direction both the direction give cancel out to be zero or greater applied forces