A ball moves in a circle at the end of a string, as shown. An illustration of a circle with an arrowhead on the circle pointing clockwise. A black dot on the top left part of the circle is a dot with 4 vectors from it. Vector z away from the center of the circle, vector y toward the center of the circle, a vector tangent to the circle and clockwise labeled w and a vector labeled x along the circle and in the clockwise direction. Which arrow represents the centripetal force responsible for this motion? w x y z.