A cart moves along a straight, level track with constant non-zero acceleration \(a\). A motion detector records the position \(x\) of the cart as a function of time \(t\), starting from \(x = 0\) at \(t = 0\) with an unknown initial velocity \(v_0 \neq 0\). To determine \(a\) from a linear fit of the data, which quantities should be plotted on the vertical and horizontal axes, and what is the relationship between \(a\) and the slope of the resulting line?