$2\mathrm{.}60$ At room temperature $(20C)$ a $0\mathrm{.}5-mm$ gap exists between the ends of the rods shown. At a later time when the temperature has reached $140C,$ determine $($a$)$ the normal stress in the aluminum rod, $(b)$ the

$\backslash$table$[[$Aluminum$,$Stainless steel$],[A=2000m{m}^2,A=800m{m}^2$