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duplaimp
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Homework Statement
In the figure on the right, a 4.0 kg ball is attached to the end of a 1.6 m rope, which is fixed at O.
The ball is held at A, with the rope horizontal, and is given an initial downward velocity. The ball moves through three quarters of a circle and arrives at B, with the rope barely under tension.
Homework Equations
K1 + U1 = K2 + U2
The Attempt at a Solution
I tried with the following:
R = 1.6m
m = 4kg
K1 = [itex]\frac{1}{2}[/itex]m[itex]v_{a}^{2}[/itex]
U1 = mgR
K2 = [itex]\frac{1}{2}[/itex]m[itex]v_{b}^{2}[/itex]
U2 = mgR
But in a solution I found it was used U2 = mg2R
Why it was used 2R and not R? The distance to use in a circle is from the center to the particle or is from the bottom to the particle?
Because as A is in a distance R from center and B too, I tried with R for both but it seems that it needs to be done using a distance from bottom