Fig. P$2\mathrm{.}19$ and P$2\mathrm{.}20$

Fig. P$2.18$

$2\mathrm{.}19$ Both portions of the rod ABC are made of an aluminum for which $E=70$GPa. Knowing that the magnitude of $P$ is $4$ kN $,$ determine $($a$)$ the value of $Q$ so that the deflection at $A$ is zero, $(b)$ the corresponding deflection of $B.$

$2\mathrm{.}20$ The rodABC is made of an aluminum for which $E=70$GPa. Knowing that $P=6kN$ and $Q=42kN,$ determine the deflection of $(a)$ point $A,(b)$ point $B.$