1. The problem statement, all variables and given/known data See attachments. 2. Relevant equations 3. The attempt at a solution In Example 2.11, why is the work for friction -6(10+Δ)? Why is it negative 6? In Example 2.12, again why is the friction -6, and then where did (Δ-d) come from? I thought Δ is the distance the spring is initially compressed, and d is the distance of its maximum extension? So why minus? And also in this example why is there a negative sign in front of the work for weight? Totally confused about orientations in this problem.