You can calculate the speed of the ball by the distance it travels divided by the time.
Length of string = 2m
Circumference of circle = 2*radius*π = 4*pi = ~12.6 meters
Speed = distance/time = 12.6m/2s = 6.28m/s
Acceleration = V²/R where the velocity at any one point is the same as the speed.
acceleration = (6.28)²/2 = ~19.72m/s²