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# Edexcel M2/M3 June 6th/10th 2013 Watch

1. (Original post by kvohra)
yes but a better way to think about it is work done by the resistance on you
This is just getting more confusing. work against resistance, work by cyclist, and ke and pe loss are all different things!
I just want to know why we're saying energy loss + wd by cyclist = wd against resistance
2. (Original post by Exams v__v)
Why 1/root2 ?
Because impulse is a vector which has magnitude and direction, so you have to do the inverse of the direction x the direction x the magnitude (sorry not the best way of explaining it)
3. (Original post by Boy_wonder_95)
First find the magnitude of the direction

Then do the inverse of the magnitude x the Impulse x the parallel vector

Couldn't you just do the first time to get root 2, and then realise to get 9 root 2 it would have to be 9(i-j)?
4. (Original post by Anonymous1717)
Couldn't you just do the first time to get root 2, and then realise to get 9 root 2 it would have to be 9(i-j)?
Oops sorry typo x_x, yh you can do it whatever way you want
5. (Original post by Boy_wonder_95)
Because impulse is a vector which has magnitude and direction, so you have to do the inverse of the direction x the direction x the magnitude (sorry not the best way of explaining it)
Haha thanks. Guess I'll just by heart that!
6. (Original post by Exams v__v)
This is just getting more confusing. work against resistance, work by cyclist, and ke and pe loss are all different things!
I just want to know why we're saying energy loss + wd by cyclist = wd against resistance
I think you are overcomplicating it. All energy loss in a system must be due to an external force opposing the motion. This force must be the resistance as there is no other force opposing the motion. This question was quite confusing as the cyclist has put a force into the system as well so the work done by the cyclist is adding to the input whereas the work resistance is taking energy out, just read this and attempt the question yourself, you should understand
7. (Original post by Olive123)
Thanks !!
No problem, and good luck tomorrow!
8. (Original post by Exams v__v)
This is just getting more confusing. work against resistance, work by cyclist, and ke and pe loss are all different things!
I just want to know why we're saying energy loss + wd by cyclist = wd against resistance
I guess ill have a go at explaining. Lets take it back to the start. The work energy principle states the change in energy is equal the work done for any situation. So think of it as a change in energy not a loss. Say we lose pe and ke for a situation over a know distance. The change in energy is the sum of the two losses and hence this equals work done.

Hopefully that helps?

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9. (Original post by Boy_wonder_95)
Because the question said there's an energy loss therefore whatever force is causing that loss must be greater than what's causing the gain

No no, because resistance causes energy loss but wd causes energy gain so the difference between Wd by R and energy loss is WD by cyclist
I think I'm beginning to understand.
10. Review exercise is killing me :|
11. (Original post by kvohra)
I think you are overcomplicating it. All energy loss in a system must be due to an external force opposing the motion. This force must be the resistance as there is no other force opposing the motion. This question was quite confusing as the cyclist has put a force into the system as well so the work done by the cyclist is adding to the input whereas the work resistance is taking energy out, just read this and attempt the question yourself, you should understand
12. (Original post by JayJay95)
I guess ill have a go at explaining. Lets take it back to the start. The work energy principle states the change in energy is equal the work done for any situation. So think of it as a change in energy not a loss. Say we lose pe and ke for a situation over a know distance. The change in energy is the sum of the two losses and hence this equals work done.

Hopefully that helps?

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Ah yes, that's the basic concept, I understood that. This question is confusing since there's extra work input by the cyclist. Wasted around 2 hours on this! -.-
13. (Original post by Exams v__v)
No problem, I had to get my teacher explain this to me yesterday
14. (Original post by kvohra)
No problem, I had to get my teacher explain this to me yesterday
So basically, energy loss in a system = wd against resistance. Tell me I'm right? :P
Haha. Good luck to you!
15. (Original post by Exams v__v)
Ah yes, that's the basic concept, I understood that. This question is confusing since there's extra work input by the cyclist. Wasted around 2 hours on this! -.-
Just looked at that question and its the perfect example of a loss in both pe and ke. The difference between the work done due to resistance and the sum of the energy losses is the work done by the cyclist

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16. (Original post by MLogan)
Review exercise is killing me :|
17. (Original post by Exams v__v)
So basically, energy loss in a system = wd against resistance. Tell me I'm right? :P
Haha. Good luck to you!
Yes energy loss in a system is work done against all forces that oppose the direction of motion, in this example it is just friction and all papers I have seen it has only been friction but they could give a dodgy question like this one so be careful
18. (Original post by JayJay95)
Just looked at that question and its the perfect example of a loss in both pe and ke. The difference between the work done due to resistance and the sum of the energy losses is the work done by the cyclist

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Yes, that's the equation I'm having a hard time in figuring. >.<
19. Let's nail M2 tomorrow! I'm hoping for 100 but need at least 91 UMS to meet my university offer!

Anybody have any last minute tips for me?

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20. whos doing M3

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