A source of sound of frequency 500 Hz is fixed to the end of a light string and is whirled in a vertical circle of radius 1 . 6 m. The string just remains taut when the source is at the highest point. An observer is located at a large distance, in the same vertical plane and at the same height of the vertical circle. Find the maximum apparent frequency heard by the observer if the velocity of sound in air is 330 m,/sec