Answer
$10.5\ m$
Work Step by Step
The angle toward the $+x^{\prime}$ axis is $18.0^{o}$ less than before, so
$\theta^{\prime}=56.0^{o}-18.0^{o}=38.0^{o}$
The magnitude of $\vec{a}$ remains the same.
Given the magnitude and new angle (in the new coordinate system), using (3-5),
$a_{y}^{\prime}=a\sin\theta^{\prime} =(17.0m)(\sin 38.0^{o})=10.5\ m$
