Final answer:
The force of friction on the bag of soccer balls is equal to the applied force, which is 28 N, because the bag is moving at a constant velocity indicating balanced forces and no net acceleration.
Step-by-step explanation:
To determine the force of friction on the bag of soccer balls, we apply Newton's second law of motion which states that the net force acting on an object is equal to the mass of the object multiplied by its acceleration (F = ma). Since the bag is moving with a constant velocity, the acceleration is 0 m/s2, and hence the net force is also zero. This implies that the force of friction exactly opposes and is equal in magnitude to the applied force, but in the opposite direction.
In this scenario, the student is exerting a force of 28 N to move the bag at a steady pace. The presence of a constant velocity indicates that the forces are balanced, meaning the frictional force must be countering the applied force. Since there is no acceleration, the force of friction will be equal to the applied force of 28 N but in the opposite direction according to Newton's third law.