$A$ player throws a ball upwards with an initial speed of $29.4\; m s^{-1}$. Choose the $x=0\; m$ and $t=0\; s$ to be the location and time of the ball at its highest point. Let the vertically downward direction be the positive direction of the $x$-axis. Determine the signs of position,velocity,and acceleration of the ball during its upward and downward motion.

(N/A) Given that the highest point is $x=0$ and the downward direction is positive:
$1$. During upward motion: The ball is above the highest point (which is $x=0$),so the position $x$ is negative. The ball is moving upwards (opposite to the positive $x$-axis),so the velocity $v$ is negative. The acceleration due to gravity $g$ always acts downwards,which is the positive direction,so the acceleration $a$ is positive.
$2$. During downward motion: The ball is below the highest point,so the position $x$ is positive. The ball is moving downwards (along the positive $x$-axis),so the velocity $v$ is positive. The acceleration due to gravity $g$ acts downwards,which is the positive direction,so the acceleration $a$ is positive.