It is not actually homework, but a physics problem I have encountered. For ease of discussion, I am attaching the question [University Physics, Young and Freedman, 12th edition] and it's solution as appeared in the solutions manual. What I don't understand is: In section (c), how can the accelerations of blocks A and B be different? They are connected by the same string. Doesn't it imply (by geometrical considerations, the string length remains the same) that the accelerations are also the same?