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james t
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Homework Statement
A ball of mass M is attached to a 1.0m pole that is pivoted on the wall at point (0,0); such that it can take the path of a circle. The ball is initially held up at rest at the point (1,0). It is then pushed with a downward force.
What minimum initial velocity must it have if it is to be able to travel all the way around the circle of radius 1.0m ?
(It must be able to get back to the point (1,0)
Homework Equations
Conservation of Energy
Ui + Ki = Uf + Kf
Centripetal Force
F = mv^2/r
The Attempt at a Solution
Due to gravity it will probably move past point (1,0) and make its way down to point (0,-1) at which I have no idea what will exactly happen then.
I guess a way to look at it is that if is able to get past point (0,1) then that is sufficient, as gravity can then take over. So what will be the minimum initial velocity if it is able to get past (0,1)
I am only guessing here but i should probably use conservation of energy, but centripetal force seems like it has something to do with this problem.
So I am going to solve for what kinetic energy at point (0,-1) that will allow it to get to point (0,1) although i have no idea if that's even right. The kinetic energy at point (0,-1) should equal the potential plus kinetic energy it has initially at point (1,0)
I set U=0 at y = -1
mgh = 1/2mv^2
2gh = v^2
(2)(9.81)(2) = v^2
6.26= V at (-1,0)
The energy it had initally must equal the energy it has at y = -1
1/2mv^2 = mgh + 1/2mv^2
v^2 = 2gh + v^2
39.2 = 2(9.81)(1) + v^2
v= 4.42 = initial velocity
I have a feeling I am wrong through. Somebody please help!
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