Lien uses a spring scale to pull a block toward the right across the lab table. The scale reads 8 N. Which force should Lien conclude is also 8 N?

Explanation:

For the block placed on the table, there are several force acting on the body along the horizontal and vertical axis. All this forces tends to keep the body in a state of equilibrium.The forces acting along the horizontal are the moving force (Fm) and the frictional force (Ff).

Frictional force are forces that acts opposite to the force that causes the body to move (moving force).

If Lien uses a spring scale to pull a block toward the right across the lab table and the scale reads 8 N, this means that the force that causes the body to move is the 8N force (moving force).

Taking the sum of force along the horizontal;

Since the body is static, max = 0

Note that the frictional force acts is the force of opposition acting in the negative x direction.

Since Fm = 8N, Ff will also be equal to 8N.

Based on the above proof, Lien can also conclude that 8 N is a frictional force

i don't know that i agree with that but what's the question ?