Calculating Gravity Using Angular Speed and Weight

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SUMMARY

The discussion focuses on calculating the force of gravity (Mg) using angular speed and weight in a vertical circular motion scenario. The user initially attempts to derive Mg by combining tension equations at the top and bottom of the swing, leading to the equation -2Mg = MV2^2/R - MV1^2/R. However, this approach is incorrect due to the omission of the angle and energy conservation principles. A correct method involves applying conservation of energy, where the kinetic energy at the bottom (1/2*m*V2^2) and the potential energy change (2mgR) must be considered to accurately calculate Mg.

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Homework Statement


Suppose I tie a ball of mass M to a string of length L and I swing the ball on the string in a vertical fashion. If the speed at the top is V1 and the speed at the bottom is V2.
Would I have:

Let T = tension in string
(top) -T - Mg = -MV1^2/R
(bottom) T - Mg = MV2^2/R

So to find Mg (the force of gravity), I would add the 2 equations to get:

-2Mg = MV2^2/R - MV1^2/R.

But somehow that is wrong?
Thanks.
 
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When the ball is moving through the bottom with velocity V2 its kinetic energy = 1/2*m*v2^2. As it moves towards the top, its kE decreases but its PE increases. At the top, KE = 1/2*m*v1^2 and rise in PE = 2mgR.Apply conservation of energy to find mg.
 

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