Fully Speed Ahead!

You've chosen wisely! Aren't you a clever one!? That was correct.

The little ball react in a similar way like the lighter (green) car. The bigger ball can be compared to the heavy (blue) car.
Now imagine how Lisa is standing in her room and how she lets the two balls drop. Die bigger ball reaches the ground at first and ...

Is there a moment when the two balls collide frontally (like the cars)? Yes? Then continue!

Remember our model experiment. What happened to the lighter (green) car after the collision with the heavier (blue) car? Now apply this principle on the situation with the two balls. Do you have a clue, now, how Lisa's experiment will end? Then you have practically reached the solution of the problem. If you are still not quite sure, choose another helpful hint.