Oops! There is another problem that I am stuck on. Here is a recap from my last thread posted this morning...I am finishing an on-line basic physics course. I am taking a self-assessment before the official on-line certification next week. Here is another problem which I am stuck on and require some guidance. A tennis ball on the end of a string travels in a horizontal circle at a constant speed of 3 m/s. The circle has a radius of 2 m and the centripetal force is 1.5 N. How much work is done on the ball each time it travels around the circle? I think that all the information given is not required. The obvious formula that has all these variables and was used thoughout the course is W=Fd. So, a force of 1.2N is exerted throughout the balls orbit. If the radius is 2 m then the circumfrance of the circle is 12.6 [2Pi(r)]. Then W=Fd...W=(1.5N)(12.6m)...W=19. I do not believe this is correct because the answer should be around 12 joules. What did I do wrong? Did I mix up formulas and units? Some guidance please.