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M2 work energy

How do I go about doing this question?
A girl and her sledge have a combined mass of 40kg. She starts from rest and descends a slope which is inclined at 25* to the horizontal. At the bottom of the slope the ground becomes horizontal for 15m before rising 6* to the horizontal. The girl travels 25m up the slope before coming to rest once more. There is a constant resistance to motion of magnitude 18N. Calculate the distance the girl travels down the slope.


http://imgur.com/a/ypS3S
This was my diagram.
The change in KE is 0. Change in P.E was 40g(25sin6-xsin25)
And the WD by resistance is 18x + 720 so I did
40g(25sin6-xsin25) = 18x + 720 and solved for x and didn't get the answer in the book
(edited 7 years ago)
Where did you get the 25m along the 6 degree slope from?
Original post by Carman3
The change in KE is 0. Change in P.E was 40g(25sin6-xsin25)

That will be negative, i.e. the increase in gravitational potential energy.
Original post by Carman3
And the WD by resistance is 18x + 720 so I did
40g(25sin6-xsin25) = 18x + 720 and solved for x and didn't get the answer in the book

Assuming that the 25m was in the question, the sign looks wrong. The WD by the resistance is negative, as it's against the direction of travel.
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Carman3
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Original post by RogerOxon
That will be negative, i.e. the increase in gravitational potential energy.

Assuming that the 25m was in the question, the sign looks wrong. The WD by the resistance is negative, as it's against the direction of travel.


25m was in the question, ive edited my original post. How would you know if the P.E is increased or decreased since we don't know what x is.
Original post by Carman3
25m was in the question, ive edited my original post. How would you know if the P.E is increased or decreased since we don't know what x is.


You can safely assume that PE2 is less than PE1 because energy has been lost in working against resistance.

PE1 - work done = PE2

Or, to arrange things as in your working:

PE2 - PE1 = -(work done)

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