Locate `c.m.` of thin , uniform semicircular wire of radius `R`.

Explanation

`dm = (m)/(pi R) R d theta = (m d theta)/(pi)`
`y_(c.m.) = (int y dm)/(int dm) = (int_(0)^(pi) R sin theta (m)/(pi) d theta)/(m) = (R )/(pi) int_(0)^(pi) sin theta d theta`
`= (R )/(pi) | - cos theta|_(0)^(2) = (R )/(pi) [ - cos (pi) - { - cos(0)}]`
`=(R)/(pi) [ 1 + 1] = ( 2R)/(pi)`