I am having a problem understanding an example in kolenkow: an introduction to mechanics. The question I have is on page 71/section 2.9 in the red cover edition. The example is telling me to find the acceleration of the end of the rope and how it is related to the acceleration of the block. I know I have to find the sum of the length of the strings and differentiate this quantity 2 times to get the acceleration. How ever in the book when the string passes one end of the pully (does not fully wrap around it). I was wondering since the 2 pulleys are circular shape there length is given by the circumference of a circle. How ever since they do not loop around the pulley (circle), they are a half circle. is that why the example has the length of string around a pully as Pie*r as opposed to being multiplied each by a constant of 2?