Answer
Unfortunately your answer is wrong.
Do the experiment again and watch carefully.
The ball moves with the cardboard (because of friction) and rolls on because of its inertia even if the cardboard has been stopped.
You already learned a little while ago, that bodies retain their state of movement because of their inertia until an external force compels them to execute another kind of movement. In this experiment, this is also proved.
Surely you know similar actions to this. While a bus is braking, you notice, that you are pushed forward. You have to hold tight strongly.
