How does the acceleration of a cart depend on the total mass if the net force is constant?
By Newton's Second Law, the acceleration of an object is proportional to the net force and inversely proportional to the mass:
a = Fnet/m
If Fnet is a constant, then as m increases a will decrease and as m decreases a will increase proportionally. That is, doubling the mass cuts the acceleration in half. Halving the mass doubles the acceleration.