physics
posted by sw on .
a stone is tied to the end of a string and is swung with a constant speed around a horizontal circle with a radius of 1.5m. if it makes two complete revolutions each second, what is the magnitude of its acceleration?
i know the answer, but i don't know how to get it. thank you!

acceleration= v^2/r
where v= 2PIr/.5sec 
thank you sooo much! :)