Question

A 0.25 kg stone tied to a 0.5 m string whirls at a speed of 4 m/s. What is the centripetal acceleration acting on the stone?

Answer 1

V^2/R is the acceleration. You don't need to know the mass unless you want the centripetal FORCE.

V = 4 m/s and 0.5 m is the radius, R.