PHYS 1P21 Lecture Notes - Lecture 17: Paper Towel, Critical Thinking, Solution Process

• School: Brock University
• Department: Physics
• Course: PHYS 1P21
• Professor: Santo D' Agostino

Document Summary

Next consider a pulley problem that is a little more sophisticated. Solution: draw three free-body diagrams; one each for the two outside masses, and another one for the central pulley. As usual, we"ll choose positive directions for each free-body diagram so that the accelerations will all be compatible. We have three equations for four unknowns, so we need another equation. Because the rope does not stretch, the accelerations are all connected, but in a way that is a little more complex than the previous problems in which there were only two blocks. So now we have four equations for four unknowns, and the problem is solvable. One way to complete the solution is to solve each of the first three equations for the accelerations and substitute the resulting expressions into equation 4: We can now back-substitute the tension into the first three equations to determine the accelerations: