A pendulum consists of a small object hanging from the ceiling at the end of a string of negligible mass. The string has a length of 0.78 m. With the string hanging vertically, the object is given an initial velocity of 2.8 m/s parallel to the ground and swings upward in a circular arc. Eventually, the object comes to a momentary halt at a point where the string makes an angle ? with its initial vertical orientation and then swings back downward. Find the angle ?.