Someone plz help plz and thx

1. Actually, mass does not affect velocity. The sum of all forces  that act on the object causes the acceleration a while the mass m resists it.

2. just say it's the force into the height that it covers from one point to another. ... (a) At point .

Explanation:

The problem is about Conservation of Energy, between Potential Energy and Kinetic energy changes.

Given is friction-less roller coaster. it is also assumed that there is no loss of energy due to air friction.

And so regardless of what path the ball takes, the work done by gravity doesn't depend on the path, it only depends upon the height through which it falls.

3. The principle of the conservation of mechanical energy states that the total mechanical energy in a system (i.e., the sum of the potential plus kinetic energies) remains constant as long as the only forces acting are conservative forces.