A uniform, slender cylindrical rod is made of a homogeneous and isotropic material. The rod rests
on a frictionless surface. The rod is heated uniformly. If the radial and longitudinal thermal
stresses are represented by $_{\sigma r}$ and $_{\sigma z}$ respectively, then
(a) $_{\sigma r}$= 0, $_{\sigma z}$ = 0 (b) $_{\sigma r\neq 0 }$,$_{\sigma z\neq 0 }$
(c)$_{\sigma r=0}$,$_{\sigma z\neq 0}$ d) $_{\sigma r \neq 0}$,$_{\sigma z \neq 0}$