# Question regarding why an example In kolenkow mechanics

1. Jan 3, 2015

### MidgetDwarf

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?

2. Jan 3, 2015

### ehild

Type in the problem text and attach a copy of the picture, please. People here are of all age from 10 to 100 I guess and from all countries of the World - most of them do not possess that book on the bookshelves, so we do not know, what is on page 71 in the red cover edition :)

3. Jan 3, 2015

### MidgetDwarf

Sorry about, thanks for informing about the procedure regarding homework help on physics forum. It turns out the my intuition was correct. Mods please close.