NatoHeadshot
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is the answer for this question wrong, the a part?
why are they taking negative for the PE after it goes through an angle thethaAttachment 624950
Attachment 624834"-mgrsino"
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RDKGames
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(Original post by NatoHeadshot)
is the answer for this question wrong, the a part?
why are they taking negative for the PE after it goes through an angle thetha
Attachment 624834"-mgrsino"
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NatoHeadshot
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(Original post by RDKGames)
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should work now
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ghostwalker
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(Original post by NatoHeadshot)
should work now
Still can't see them - "Attachment not found" comes up.
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NatoHeadshot
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(Original post by ghostwalker)
Still can't see them - "Attachment not found" comes up.
does this link not work? https://www.thestudentroom.co.uk/att...hmentid=624950
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ghostwalker
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(Original post by NatoHeadshot)
does this link not work? https://www.thestudentroom.co.uk/att...hmentid=624950
That worked.

PE is negative because they start from P(where they've assigned the PE to zero) and the object is projected downwards, hence the PE is -r\sin\theta \times mg
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NatoHeadshot
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(Original post by ghostwalker)
That worked.

PE is negative because they start from P(where they've assigned the PE to zero) and the object is projected downwards, hence the PE is -r\sin\theta \times mg
how can energy be negative
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ghostwalker
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(Original post by NatoHeadshot)
how can energy be negative
For clairty: We're talking about gravitational potential energy here, not kinetic.

Potential energy is measured relative to a reference point. In this case they've taken the position halfway up the circle as the zero point, hence any point below that has negative potential energy.

Potential energy is a measure of the work done in going from the reference point to your desired point. If that point is above the reference, then you have to do work to the mass and it has a +ve potential energy. If it's below the reference point, then the mass is doing work, losing energy (converted to KE if in free fall), and we have -ve potential energy.

The important value is the loss or gain in potential energy going from one point to another.

With P as the reference point:

PE before =0, PE after = -mgrsin(t)
(t for theta). So loss in energy is 0 - (-mgrsin(t))= mgrsin(t)

If we take the bottom of the circle as the reference point:

PE before (at P) is r, PE after = r-mgrsin(t)
Loss in PE = r - (r-mgrsin(t)) = mgrsin(t) as before.
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