Final answer:
The coefficient of friction for the surface is approximately 0.4306, and when an extra weight is added to the block, the required force to push them remains unchanged at 7.2 N, which implies that the weight of the added block is 0 N.
Step-by-step explanation:
The coefficient of friction can be determined using the relationship between the frictional force and the normal force. Based on Newton's second law, if a block is moving at a constant velocity on a horizontal surface, the net force acting on the block is zero. This means that the applied force to move the block is balanced by the frictional force. As given, a force of 3.1 N is required to move the initial 7.2 N block at constant velocity, implying that the frictional force is 3.1 N.
The coefficient of friction (μ) is calculated as the ratio of the frictional force (f) to the normal force (N). In this case, μ = f / N = 3.1 N / 7.2 N = 0.4306.
When an additional weight (W) is added, and the total force needed to move the block at constant velocity is still 7.2 N, this indicates that the total weight of both the block and the additional weight is balanced by the normal force. The frictional force is equal to the coefficient of friction times the normal force, which we can write as f = μN = 7.2 N. However, since 7.2 N was also the weight of the block without the additional weight, the additional weight W adds no net force; thus, W must be zero Newtons.