From Newton's first law of motion we understand that an object moves at a constant velocity only when all the forces are balanced. By definition, inertia is a resistance to a change in motion. Also by definition, mass is a measure of inertia. Thus the extend of resistance to a change of motion is determined by the mass of an object, which is measured in kilograms. If you double the unbalanced force on an object of a given mass the acceleration will also be doubled.
Weight is the force of gravity acting on a mass.
As discussed in question three, inertia is a resistance to a change in motion. Also by definition, mass is a measure of inertia. Thus the extend of resistance to a change of motion is determined by the mass of an object, which is measured in kilograms. From Newton's third law of motion we understand that every force is immediately matched by a second force that is equal in magnitude and opposite in direction. So, the car pushes on the road and the road pushes back on the car, which accelerates it over the road.