Looking at the force diagram above, there is only a component of the tension force acting in the horizontal direction. This means the net horizontal force can't be zero.

Consider the block shown above supported by feet at A and B that is at rest on a rough floor. A horizontal force P is applied to the right on the block. As the magnitude of P is increased slowly, two ...

The horizontal forces are equal in size and opposite in direction. They are balanced, so the horizontal resultant force is zero. This means that there is no horizontal acceleration.

The horizontal forces are equal in size and opposite in direction. They are balanced, so the horizontal resultant force is zero. This means that there is no horizontal acceleration.