Final answer:
To find the force of friction acting on a 50 N box pulled with an 80 N force, we would subtract the net force (which includes the effect of friction) from the applied force. However, with the provided information, we cannot determine the exact friction force without knowing the box's acceleration or mass. If the acceleration results in a net force of 30 N, the friction force would be 50 N.
Step-by-step explanation:
If a 50 N box is being pulled by a rope with a force of 80 N and the box accelerates, the amount of friction acting on it must be such that the net force accounts for the acceleration observed. To determine the force of friction, we use Newton's second law of motion (F = m*a). In this case, we are provided with the forces acting on the box but not the acceleration or mass explicitly.
However, if we understand that the net force is the difference between the applied force and the frictional force, we can deduce that the frictional force is the applied force minus the net force (since the net force includes the effect of friction). Assuming that there is acceleration, this means that the net force is not zero, and the applied force is greater than the frictional force. Thus, the force of friction acting on the box is 80 N (applied force) - net force (unknown value). Without the box's acceleration or mass, we can't solve for the exact value of friction. But, if the net force was indeed equal to 30 N (option a), then the force of friction would be 50 N, because 80 N (applied force) - 50 N (friction) will result in a net force of 30 N responsible for the acceleration of the box.