Force exerted on keys revolving in a circle at 3 revolutions per second

[skajdhfkjsdfh]

Please try this problem. I am really stuck!

My keys of .3 kilograms revolve uniformly in a circle attached by a cord of 0.8 m long. The keys make 3 complete revolutions in one second. Find the force exerted on them by the cord.

 

[Dick]

You need to tell us what you know and where you are stuck. What do you know about the acceleration of an object in circular motion? What do you know about the relation between acceleration and force?