# Quick Question

You have a cylinder (with radius R) rolling horizontally on a surface with kinetic friction of u(mu). I understand that the horizontal acceleration is u*g b/c:

ma = u*(mg)
a = u*g

and then you have

a = r (alpha_z)

thus I'd figure alpha_z is just u*g/R, but the book gives a solution of:

-2 u*g/R

Basically, what's the reasoning?