Here is a strange test question I really don't get:
A ball falls freely from a certain height, and due to air resistance it will reach a certain terminal velocity (assuming there is a normal gravitational acceleration going on all the time). Then it hits the ground, and bounces back without loss of energy.
Question : what is the acceleration on the ball immediately after it bounced?
The answer is $2g$ (2 times gravitational acceleration), but the explanation is not included.
Note: This is a question from the Physics Olympiad!