Answer
$a).$ Angle of the ball should be backwards from vertical.
$b).$ $0.51m/s^{2}$
Work Step by Step
a). The angle of the ball is backward from vertical.
As the RV starts moving or accelerating forwards, the ball moves backward due to inertia.
b). The ball makes $3^{\circ}$ with vertical.
Thus, by both vertical and horizontal components,
$Tsin\theta=ma$
$Tcos\theta=mg$
or, $tan\theta=\frac{a}{g}$
$a=gtan\theta=9.8\times tan3^{\circ}=0.51m/s^{2}$
