The definition of work in physics is: the force received by an object times the displacement of the object in the direction of the force. That is, work is the effect of force accumulation in space.

Formula: W=FScosB(B stands for the included angle between force and displacement. Attention and displacement are vectors, but work is scalar, which can be compared to vectors and cross product in mathematics.

According to this definition, the answers are 300J 0J respectively.

According to Newton's second law, the force of the object is balanced at this time.

Friction equals tension.

Mathematically speaking, the work done by overcoming friction is equal to the work done by pulling force.