What is the correct speed to keep the cylinder at rest?

[J-dizzal]

Homework Statement

A puck of mass m = 1.00 kg slides in a circle of radius r = 17.0 cm on a frictionless table while attached to a hanging cylinder of mass M = 3.70 kg by a cord through a hole in the table. What speed keeps the cylinder at rest?

http://edugen.wileyplus.com/edugen/courses/crs7165/art/qb/qu/c06/q55.jpg
[/B]

Homework Equations

F=ma, a=v²/r[/B]

The Attempt at a Solution

I don't see why 0.785m/s is incorrect. thanks.[/B]
http://i1164.photobucket.com/albums/q562/falsovero/20150630_150006_zpsk3vkjyjj.jpg

 

[Orodruin]

The radius is 17 cm, not 1.7 cm.

 

[J-dizzal]

thanks, what an elementary mistake.