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Finding Potential Energy of a Swing When the Ropes Are Horizontal? 
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#1
Apr1412, 12:29 PM

P: 1

1. The problem statement, all variables and given/known data
A 45.0 kg child is in a swing that is attached to ropes 1.90 m long. The acceleration of gravity is 9.81 m/s2 . Find the gravitational potential energy as sociated with the child relative to the child’s lowest position under the following condi tions: a) when the ropes are horizontal. Answer in units of J. 2. Relevant equations Height of a pendulum: h=L(1cos(θ)) Potential Energy PE=mgh 3. The attempt at a solution So first I found the height of the swing at a horizontal position which I assumed is as at 90°. h=L(1cos(θ)) 2.75m=1.9(1cos(90)) Then I used that height and put it into the formula for potential energy PE=mgh 1213.99 J? = (45)(9.81)(2.75) but the online homework interface I have to use to input my answer tells me this isn't correct. I was wondering if maybe my answer isn't in Joules, do I need to convert something. Any help would be greatly appreciated. I realized my problem, i had my calculator in radian's sorry for the stupid question, I'd delete the question if i can find out how 


#2
Apr1512, 08:25 AM

HW Helper
P: 6,202

The ropes are 1.9 m long while the height you used is 2.75 m. How exactly did you get 2.75 m using h = L(1cosθ)?



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