The movement of man when resultant horizontal force is 0N is that Man is moving at constant velocity
Since Man increases force A. the thing that happens to force B and the movement of the man are:
- Man - accelerate so force B increases
- until force B = force A.
- Man moves at higher constant velocity
If the resultant horizontal force acting on the man is zero, then the man will not accelerate in the horizontal direction. This means that the man will continue to move in a straight line at a constant speed. The man may also be rotating, but this rotation will not change the man's horizontal velocity.
So, If the man increases Force A, then the resultant force will no longer be zero. This means that the man will accelerate in the direction of Force A. The magnitude of the acceleration will be equal to the ratio of the force to the mass of the man.