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M2 Energy and Work Edexcel question Watch

1. This is a question from the edexcel Heimann book. The solution is not in Physics and Maths .com and I can get the CD to work.
3C Q18:
A girl ans her sledge have a combined mass of 40Kg. She tarts from rest and descends a slope which is inclined at 25 degrees to the horizontal. A the bottom of the slope becomes horizontal for 15m before rising at 6 degrees to the horizontal. The girl travels 25m up the slope before coming to a rest once more. There is a constant resistance to motion of a magnitude 18N. Calculate the distance the girl travels down the slope. I shall include my working. I got 10.594m when the book says 11.8m. Any help would be greatly appreciated.
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2. I got 11.8m

All you need to do is consider the energy changes.
So you have the energy at the start when the girl is at the top of the slope.
The GPE is where d is the distance up the slop the girl is.
The total work done is 18 x (d+15+25)=18(d+40)
The GPE gained going up the second slope is .
So now set up an equation linking all this information together using the principal of conservation of mechanical energy and find d.
3. (Original post by B_9710)
I got 11.8m

All you need to do is consider the energy changes.
So you have the energy at the start when the girl is at the top of the slope.
The GPE is where d is the distance up the slop the girl is.
The total work done is 18 x (d+15+25)=18(d+40)
The GPE gained going up the second slope is .
So now set up an equation linking all this information together using the principal of conservation of mechanical energy and find d.
Thank you very much for your help. Looking back I had the right idea but used the wrong numbers. Thank you.

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