Centripetal acceleration can be calculated through the equation:
Ac=V^2/r
V is given as 25 m/s, and r can be calculated through using C=pi•d, but we need the circumference first.
25 meters/s to make one quarter turn = 100 meters total circumference
C=pi•d
100=pi•d
d=31.83 meters
Notice that the equation for Ac asks for radius, which can be calculated by dividing the diameter by two (31.83/2 = 15.92).
Ac=V^2/r
Ac=(25^2)/15.92
Ac=39.26 Newtons
The centripetal acceleration of this object would be approximately 39.26 Newtons (re-run this calculation set with a calculator because rounding was heavily utilized).