- #1

gibson101

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For the following question, I am given the weight of a ball being twirled on a string, the radius of the string, and the velocity. And I am asked to calculate the tension of the string when the ball is at the top of it's path, and the bottom of it's path. I know that tension is a centripetal force so I used the formula Fr=mv^2/r and then added or subtracted mg (normal force = mg). I don't understand why I am subtracting mg when the ball is at the top, nor adding at the bottom, since the centripetal force and normal force are in opposite directions at the bottom then I would think I would subtract them then. And now that I think about it, there isn't a normal force, cause the normal force is always perpendicular to the surface that the object is on, but there is no surface! Can someone please enlighten me on this! Thanks.

((.3)(3.9)^2/(.8)) + or - (.3)(9.8) = 8.6 or 2.76 Newtons

((.3)(3.9)^2/(.8)) + or - (.3)(9.8) = 8.6 or 2.76 Newtons