Question on: SS2 Physics - Mechanics - Motion in a Plane

The centripetal acceleration of an object in uniform circular motion is given by the formula: acceleration = (v2) / r, 

where v is the velocity of the object and r is the radius of the circle. Since the stone completes one revolution in 4 seconds, its velocity is given by 

v = (2πr) / T = (2π x 2) / 4 = 2π m/s. 

Plugging in the values, we get acceleration = (2π2) / 2 = 8 m/s2.