How Is Total Work Calculated for Blocks on a Pulley System with Friction?

[lil_50]

Homework Statement

Two blocks are connected by a very light string passing over a massless and frictionless pulley. The 20.0-N block moves 75.0 cm to the right and the 12.0-N block moves 75.0 cm downward.

1. Find the total work done on 20.0-N block if u_s=0.500 and u_k=0.325 between the table and the 20.0-N block.
2. Find the total work done on 12.0-N block if u_s=0.500 and u_k=0.325 between the table and the 20.0-N block.

Homework Equations

The Attempt at a Solution

Well the first thing we were supposed to do was find the work done if there was no friction and for the first I got the answer to correctly be 5.625J and the second to be 3.375J. So since the system was already moving I tried to just take the normal force multiplied by the coefficient of kinetic energy but that answer was incorrect. PLEASE HELP.

 

[Doc Al]

So since the system was already moving I tried to just take the normal force multiplied by the coefficient of kinetic energy but that answer was incorrect.

Not sure what you did. Multiplying the normal force times the coefficient of kinetic friction will give you the friction force. What then?

How did you find the answer to part 1?