2. A child swings back and forth on a swing with no friction or air resistance between points X and Z, as shown. Point Y is the lowest point in the swing, where height is zero. Which of the following is equal to the kinetic energy of the child at point Y?
(A) The kinetic energy of the child at point X.
(B) The kinetic energy of the child at point Z.
(C) The potential energy of the child at point Y.
(D) The potential energy of the child at point Z.
