1. The problem statement, all variables and given/known data Hi, sorry, I am not good at writing English, but I am trying. I hope that someone helps me solve the following problem. http://hodol.kr/q.jpg [Broken] Please refer to the figure above. A stick(AB) of length 5 is leaning against the Wall(AO) and a string(CO) is tied at the origin(O) and at a point(C) on the stick(AB). There are no frictional forces of wall and of floor so that the stick was sliding down. However, when the length of OB is 3, the sliding of the stick have been stoped. Figure out the strength of the tension force on the string(OC). 2. Relevant equations 3. The attempt at a solution Well, I tried to solve the problem, but I could not. I think that the point C moves along some elliptic curve with origin at O. Therefore, the tension force on the string(OC) may be the same as the centripetal force of the movement along the elliptic curve and it makes balance with centrifugal force. Am I right, or please show me the solution. Have a good day! Thanks.