QR: Rolling Revisited and Gyroscope

Here are tomorrow's quiz questions. For the first one, consider carefully the consequence of the energy conservation, including the rotational kinetic energy, if applicable.


This question is related to the Newton's equation which says tau = dL/dt. The point here is that the gyroscope is spinning very fast and the hand is exerting a small torque to change L = I omega. The answer is quite non-intuitive, due to the nature of the angular motion.