Steve and Valerie measure the time it takes for two smooth aluminum spheres to roll down a ramp, and they make a histogram analogous to that made by Dyan and Kelly. The radii of the two spheres are the same (at least, to the precision of their measurement device), but one sphere is hollow while the other is solid.

a. Is this a reasonable test of the effect of mass on the acceleration of a sphere? If not, what would be?
b. Is this a reasonable test of the effect of hollowness? If not, what would be?