Move over Jeff Bezos, this invention is about to make you the richest person in the world. You have just invented the OyOy (that's YoYo spelled backwards). It is the very latest in home safety and so easy to use!

If your building is on fire, simply reach out and grab the cord on the OyOy and you will be lowered safely toward the ground at a low velocity. The OyOy has a total mass M = 95.0 kg and is shaped like a cylinder of radius R = 0.940 meters. The secret to the operation of the OyOy is its patented shaft whose radius is only r = 0.0900 meters. The cord is wound around the small shaft and this is the secret to your low velocity.

We will use the approximation that the shaft is of negligible mass compared to the total. This means that you can treat the entire OyOy as though it is a solid cylinder with mass M and radius R. Imagine that a customer of mass m = 78.5 kg is using the OyOy and begins his decent from an initial height of y0 = 12.55 meters.

Find velocity of customer at ground.