Here is a physics problem- I know a= v^2/ r:
The centripetal force apparatus consists of 450 g (.45kg) hanging mass located 22.0 cm (.22m) from the center of the vertical shaft. The time for 5 complete revolutions is 4.50s. Assume the speed is constant and find centripetal acceleration and centripetal force. (f= mv^2/r)

Help please!