Figure I
Figure II
1981M2. A swing seat of mass M is connected to a fixed point P by a massless cord of length L . A child also of mass M sits on the seat and begins to swing with zero velocity at a position at which the cord makes a 60∘ angle with the vertical is shown in Figure I. The swing continues down until the cord is exactly vertical at which time the child jumps off in a horizontal direction. The swing continues in the same direction until its cord makes a 45∘ angle with the vertical as shown in Figure II: at that point it begins to swing in the reverse direction. With what velocity relative to the ground did the child leave the swing?