Solution

What happens with the balloon and the football? (Click onto the right answer).

a) Nothing happens. They both stay where they are because there is not any force acting on them.

b) They both move backwards (to the the rear window), because the force of inertia pushes mobile things backwards against the driving direction while braking.

c) They both move forward (to the windscreen), because mobile things still roll in the driving direction while braking because of their inertia.

d) Only the football moves forward because of its inertia. The balloon acts differently because of its small mass, it moves backwards.