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# The Official Edexcel M2 Revision Thread! (24/06/05 AM) watch

1. (Original post by endeavour)
But I don't understand what the mark scheme's done.
what does it say?
2. (Original post by Widowmaker)
what does it say?
λM*4a = M(44a/15)
3. does anyone have the January 2002 markscheme please?
4. (Original post by endeavour)
λM*4a = M(44a/15)
5. does any have the mark scheme 4 jan05 plz!?
6. (Original post by topdude)
does any have the mark scheme 4 jan05 plz!?
iv got it..pm me ur email addy...quick plz, im leavin in another min!
7. with the January 2004 paper, I have decided that I found question 5 the most aggrevating
8. (Original post by KAISER_MOLE)
with the January 2004 paper, I have decided that I found question 5 the most aggrevating
I found that part alright.
6)c took me a while.
9. (Original post by Widowmaker)
not strictly true.
When the car brakes, the tow-bar pushes the trailer and car apart from each other, this is the thrust of the tow-bar.
If you did it as a tension it would be acting in the opposite direction.
Could you explain further... why would the tow-bar push the trailer and car in the opposite direction, what is thrust and why does it act in the opposite direction...???

i tried doing the question thinking of it as tension in the 1st place and it didn't work because it gives a negative number... i'm assuming that your right must that thrust act's in the opposite direction but i need a bit more of an explanation as to why
10. (Original post by Revenged)
Could you explain further... why would the tow-bar push the trailer and car in the opposite direction, what is thrust and why does it act in the opposite direction...???

i tried doing the question thinking of it as tension in the 1st place and it didn't work because it gives a negative number... i'm assuming that your right must that thrust act's in the opposite direction but i need a bit more of an explanation as to why
When the car is moving, the trailer also moves at the same speed as the car. The tension in the tow-bar provides the motion of the trailer.

When the car brakes, the trailer doesn't brake it continues moving, the thrust in the towbar decelerates the trailer so it doesn't collide into the car.

Think of the tow-bar as a spring. When you compress the string too much, it pushes back on you. This is an example of newton's third law. You exert a force on the spring, the spring exerts an equal but opposite force on your hand. This is the thrust in the spring.
11. (Original post by Widowmaker)
When the car is moving, the trailer also moves at the same speed as the car. The tension in the tow-bar provides the motion of the trailer.

When the car brakes, the trailer doesn't brake it continues moving, the thrust in the towbar decelerates the trailer so it doesn't collide into the car.

Think of the tow-bar as a spring. When you compress the string too much, it pushes back on you. This is an example of newton's third law. You exert a force on the spring, the spring exerts an equal but opposite force on your hand. This is the thrust in the spring.
and if you want a formula, just do:
thrust = -1 X tension
12. (Original post by Widowmaker)
When the car is moving, the trailer also moves at the same speed as the car. The tension in the tow-bar provides the motion of the trailer.

When the car brakes, the trailer doesn't brake it continues moving, the thrust in the towbar decelerates the trailer so it doesn't collide into the car.

Think of the tow-bar as a spring. When you compress the string too much, it pushes back on you. This is an example of newton's third law. You exert a force on the spring, the spring exerts an equal but opposite force on your hand. This is the thrust in the spring.
hang on... call me stupid but if you stretch a string you have a force pulling the spring back together... so this force is tension

if you push spring closer together then there will be a force acting oppositely on the spring this is the thrust... yeah?
13. (Original post by Revenged)
hang on... call me stupid but if you stretch a string you have a force pulling the spring back together... so this force is tension

if you push spring closer together then there will be a force acting oppositely on the spring this is the thrust... yeah?
that's right.
14. so when the car is moving normally there is a tension pulling the trailler and an equal an opposite tension acting on the car

when the car is breaking... the car slows down but the trailer is going forward... this is like a compressing spring. This means there will be a thrust pulling the trailer back and a thrust pushing the trailer forwards

so this means that tension and thrust are the opposite of each other???
15. grazie mille!!!
16. (Original post by Revenged)
so when the car is moving normally there is a tension pulling the trailler and an equal an opposite tension acting on the car

when the car is breaking... the car slows down but the trailer is going forward... this is like a compressing spring. This means there will be a thrust pulling the trailer back and a thrust pushing the trailer forwards

so this means that tension and thrust are the opposite of each other???
not exactly since the situation has changed. (ie thrust in new situation is not alike to tension from old situation)
seeing as you are getting thrust you should do it the properway

for others that dont understand thrust, i would suggest (in the new situation) use tension as you normally do, then at the end do -1xtension
17. (Original post by Revenged)
so when the car is moving normally there is a tension pulling the trailler and an equal an opposite tension acting on the car

when the car is breaking... the car slows down but the trailer is going forward... this is like a compressing spring. This means there will be a thrust pulling the trailer back and a thrust pushing the trailer forwards

so this means that tension and thrust are the opposite of each other???
yes.
That question won't come up again (its highly unlikely anyway) so don't worry about it too much.

Coefficient of restitution will almost definitely come up.
18. have you got any tips for these impossible range of value of e questions

so far no one has been very helpful

and my technique of trial and error... basically just look at the numbers for any way of getting an inequality that is in between 0 and 1 works very rarely
19. (Original post by Widowmaker)
What do you guys think of m2 jan 04?
Hardest paper I've done so far.
just did it and did NOT like it. bout 3 parts i dont understand.

question 3b) why do they ignore gravitational forces and potential energy when finding µ?
question 4b) how have they found µ? the answer doesnt make sense
question 7e) where did the forces 'S' and 'R' come from?

if ne1 has any idea what im talking about, would appreciate any help. im having a dumb day today
20. (Original post by Revenged)
have you got any tips for these impossible range of value of e questions

so far no one has been very helpful

and my technique of trial and error... basically just look at the numbers for any way of getting an inequality that is in between 0 and 1 works very rarely
if direction of a particle is changed (normally the case), then V < 0 or V > 0 depending on your positive direction.

so if v = ½(1-3e)u

v < 0
=> ½u - 3eu/2 < 0
=> ½u < 3eu/2
=> u < 3eu
=> 3eu > u
=> e > u/3u
=> e > 1/3

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