Question

A girl is whirling a ball on a string around her head in a horizontal plane. She wants to let go at precisely the right time so that the ball will hit a target on the other side of the yard. When should she let go of the string?

Answer 1

Answer:

The girl should leave the string a time when the ball is at a position tangent at that point of the circle passes through the location of target.

Explanation:

The direction of an object moving in circular path changes endlessly with time. The direction of the object at some extent are within the direction of tangential drawn to the circle at that point,  

The  centripetal force on the ball becomes zero once the girl leaves the string. hence, the ball can go into the direction tangential to the circle at the point whenever she left the string.