Only if you push it. On a perfectly flat surface, in neutral it will not roll without assistance.
If it's parked on a flat it should not roll at all
you are a cone
yes
So it doesn't roll off when you place it on a flat surface.
A face.
either the e-brake did not release or it is still in gear
A smooth and flat surface with minimal friction, such as a polished marble floor, will allow a ball to roll the fastest. The lack of friction will reduce resistance and enable the ball to maintain its speed for longer distances.
The object described is a cone. A cone has one vertex (the point where the flat face meets the curved surface) and one flat face (the circular base). Due to its shape, a cone can roll along a flat surface smoothly.
Put it in neutral and push it.
A cone fits the description.
Most likely a bad brake calpier.
Because you did not set the parking brake. When it rolls in gear, it will slowly be turning the gears and the pistons in the engine, so it won't roll as easily as when it is in neutral, but it will still roll.