After a discussion with our teacher, we concluded that the physics of the game were not satisfying. The balls were jumping all over the place and were annoying to crash into, because they would just jump and get on top of the car. With this, the solution applied was disabling the Y axis for the balls, making them enable to "jump" at all.

Along with the axis change, a physics material was added to the balls, car and table, so they would have more bounciness, making the car and the balls bounce off the table's walls with more force. The material also gave the objects a bit more friction.