Answer:-
Force on AB, Fab = P+10
Area of AB , Aab = π (1.25)^2/4 = 1.22718 m^2
So stress on AB is , σab = Fab/Aab = P+10/1.22718
For the rod BC :-
Force on AB, Fab = P
Area of AB , Aab = π (0.75)^2/4 = 0.44179 m^2
So stress on AB is , σab = Fbc/Abc = P/0.44179
Now, σab= σbc
P+10/1.22718 = P/0.44179
So, the value of force P = 12.7325 kips