Problem: A 5 kg block aluminum block slides on a steel table as shown. The pulley is very light and frictionless. Find the acceleration and the tension in the cord.

Solution: There is no doubt about the direction of the motion. Serway's table 5.2 on page 126 gives the coefficient of kinetic friction as 0.47. Here are the free body diagrams:

I've chosen the directions as positive in the direction of the acceleration, for the reasons mentioned in module 1.

Adding these two equations to eliminate T, I get: