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# circular motion problem watch

1. https://oxfordpat.wordpress.com/oxfo...2-question-17/

how do I know that F is acting inwards rather than outwards? Also can someone explain the significant of the F greater than or equal to 0? I dont understand how it affects the object touching or not.
2. (Original post by alvan15)
https://oxfordpat.wordpress.com/oxfo...2-question-17/

how do I know that F is acting inwards rather than outwards? Also can someone explain the significant of the F greater than or equal to 0? I dont understand how it affects the object touching or not.
F here means N, normal reaction from surface against object; it points inward. If you sum a set of forces, net inward result is called centripetal force (Fc).

At T: N + mg = Fc = mv^2/r => N = m(v^2/r - g)

N is ≥ 0 if object touches track, else it falls.
KE = 0 at T => N < 0 => object falls vert (Ans B)

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