Remember the golden rule of force: Force=mass x acceleration. / / / Divide both sides by mass and you have. Acceleration=force/mass. / / / Now the small mass has small force on it, so acceleration=1force/1mass. The double mass has double force on it, and acceleration=2force/2mass. / / / Simplify that fraction: acceleration=1force/1mass. Same acceleration even though the mass is different.