[问答题]
A girl is whirling a ball on a string around her head f/o :zgqy t:+min tj:eb ,g/;zejls (xx -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. Whez(,b:s-jjeex;/tx g ln should she let go of the string?
