A flat uniform disk of radius 2R has a hole of radius R removed from the center. The resulting annulus is then cut in half along the diameter. The remaining shape has mass M. What is the moment of ...

Why it is much more difficult to balance yourself on a bicycle that is at rest than on one that is rolling?
Balance on a bicycle is a matter of constantly correcting against falls, and it's easier when the speed is higher because the inertia of moving forward overcomes the need for corrective actions.
An interesting video on stability while in motion: