for that problem, since its a 4 marker, 2 marks would be dedicated to the correct calculation and 2 marks dedicated to the explanation. for the describe bit you'd probably just define centripedal force and how the angle theta changes based on the motion of the car. i.e. equal and opposite forces, the ball swings right when the car turns left etc.,
the calculation bit can be derived with tension, and since we're given that its on an angle:
View attachment 45965
its also a good idea to reference proportionality, saying that v is directly proportional to the radius of the turn and theta