A tube of aluminium of 40 mm external diameter and 20 mm internal diameter is snugly fitted on a solid steel rod of 20 mm diameter .The composite bar is subjected to an axial compressive force P.If the stress on steel bar is 70 $$\frac{N}{mm^{2}}$$, the stress in the aluminium tube and the corresponding the value of P will be :$$(E for steel : 2 \times 10^{5} \frac{N}{mm^{2}} and E for aluminium 7 \times 10^{4} \frac{N}{mm^{2}} )$$