If Mr. Kirwan's pet Fluffy the Wonder Hamster rides his unicycle at a rate of 5m/s to the

north on a flatbed train car. Under what conditions do you see him moving at 5 m/s?

The condition that would induced the seer or observer to see that the pet hamster is moving at 5 m/s is when the train is also moving at that speed. This is because the unicycle will only allow limited vision to the seer thinking that the pet hamster is not moving at that speed.