Two circular rods, both of length l and having the same diameter, are placed end to end between rigid supports with no initial stress in the rods. the coefficient of linear expansion and young's modulus for rod a are αa and ya respectively; those for rod b are αb and yb respectively. both rods are "normal" materials with α> 0. the temperature of the rods is now raised by δt.

what is the stress f/a in the rods after heating? express the stress in terms of ? a, ? b, ya, yb, and ? t.