Centripetal Acceleration and Forces in Uniform Circular Motion Activity 1: This is a challenging problem that will require putting together several Big Ideas to answer the question. Consider the following situation: A ball of mass = 0.4 kg is attached to one end of a string. The other end of the string is attached to the ceiling. The ball is set in motion in such a way that it traces a horizontal circle of radius = 0.5 m and moves at a constant speed = 1.25 m/s