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Gravitational Potential Energy of a rope

The problem states that: "Bruce stands on a bank beside a pond, grasps the end of a 10.0m long rope attached to a nearby tree and swings out to drop into the water. If the rope starts at an angle of 35 degrees with the vertical, what is Bruce's speed at the bottom of the swing?
Variables:
angle of the rope with the vertical: 35 degrees
Length of rope: 10m


I'm trying to use the equation for the change in gravitational potential energy, where the Work due to gravity = -mg(yf-yi) which is equal to Kf-Ki, and therefore -mg(yf-yi)= -1/2mvi^2+-1/2mvf^2. With the initial velocity as 0 and the masses canceling out the solution should be Vf=[tex]\sqrt{}[/tex]2g(yf-yi).



I am apparently either setting up the question wrong, or going about it wrong all together. I'm pretty much stumped as to what I'm doing wrong and how to fix it. If someone could point me in the right direction I'd be ecstatic...
 

Answers and Replies

Tom Mattson
Staff Emeritus
Science Advisor
Gold Member
5,474
20
There is nothing wrong with your setup. Why do you think that there is?
 
I thought I was doing it right, but the website we use to submit our homework wasn't accepting the answer I got from the formula. Thanks.
 
Tom Mattson
Staff Emeritus
Science Advisor
Gold Member
5,474
20
I thought I was doing it right, but the website we use to submit our homework wasn't accepting the answer I got from the formula. Thanks.
You must be making a computational error. If you post your calculations, we can find your mistake.
 
That's okay. I think I know what happened. I probably rounded off to the wrong number is all. A similar thing happened in another homework assignment after I posted the question. Thankfully I caught that one before I ran out of chances to answer the question.
 

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