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My study mate and I have been trying to figure this one out but have not had success. This is the problem we would appreciate to get some help with:

A ball with mass of 20 grams is attached to a robe and is revolving vertikal in a circle. There is no energy beeing added to it. At the ball highest point, a force of 0.2 Newton is pulling on the robe. What is the force on the ball"s lowest point?

The statet result says 1.4 Newton.

The most logical way of solving this problem is that at the highest point, the sum of all forces is the the centripedal force minus the gravitational force:

[tex] 0.2 N = - mg + m\omega^2r [/tex]

At its lowest, the sum of the forces that act on the ball should be

[tex] F = + mg + m\omega^2r [/tex]

Is this assumption right? With those to equations we get 0.4 Newton, which sounds actually good to me. Maybe my professor is wrong ?!

Any help will be appreciated!

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# Stone revolving vertical

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