A cylindrical bar of aluminum $($Young$\text{'}$s modulus E and Poisson's ratio v$)$ has a diameter do$.$ What uniaxial tensile unit load o in the elastic domain must be applied to it to produce an elongation Ad in the transverse direction? d$\_\{0\}=20$~mm et $\backslash$Delta d$=5\mathrm{.}10^\{-3\}$ mm$.$