A uniform hollow disk with inner radius 30cm and outer radius 60cm has two pieces of thin wire wrapped around its outer rim and is supported from the ceiling. Suddenly one of the wires breaks and the remaining wire does not slip as the disk rolls down. Use conservation of energy to find the speed of the center of this disk after it has fallen a distance of 2m.

You have two photos of a person walking. one shows the person at the corner of third and main streets, the other shows the person at the corner of tenth and main streets. there are lampposts at every corner in this town, and the first picture shows it to be 10: 32: 00 exactly. the second picture shows it to be 10: 49: 30. you know three facts: (1) all of the clocks are synchronized; (2) there are exactly 12 equal-sized blocks per kilometer in this town; and (3) the streets that cross main in this area are numbered consecutively, with no interruptions. what is the person’s average speed in kilometers per hour?