1. The problem statement, all variables and given/known data In an experiment, I measured the effect of mass on the acceleration of a cart, rolling down a leveled air track. I then graphed acceleration vs. mass (m'), where: m' = m / (M+m); M = mass of the cart, m = hanging mass, which was increased with subsequent trials. 2. Relevant equations m' = m / (M+m) 3. The attempt at a solution The equation of the line that I got when I graphed this relationship, is y=9.855x-0.017. I am trying to figure out what the "meaning" of y-intercept value means. I know that at the y-intercept, the x-intercept (in this case, the mass m') is zero... but this doesn't make sense in the context of this problem. Doesn't this essentially mean that when mass is zero, then acceleration is -0.017m/s/s? Theoretically, if mass is zero, then acceleration is zero.