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# Edexcel - M3 - 18th May 2016 watch

1. (Original post by BBeyond)
June 12 4b what a horrible q such retarded angles
It's a throwback to m2 which is a severe problem for me as i was pretty **** at them at the time and that was a year ago...
2. (Original post by physicsmaths)
I can't think of one using normal principles. It uses FP3 the ideas I am thinking of.

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I did FP3 last year and remember some of it lol. Can you explain more?
3. (Original post by physicsmaths)
I can't think of one using normal principles. It uses FP3 the ideas I am thinking of.

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You can do it with a hemisphere of radius r+delta r - one of radius r but it's ugly
When calculating the time in SHM between two points, remember to use x=Acos(wt) if the particle starts at the amplitude position and vice versa, use x = Asin(wt) if it starts at the equilibrium position. And always make sure x is the displacement from the origin (I sometimes make the mistake in thinking that it's the displacement from where the particle starts the SHM (which is usually the amplitude) but it's always from the origin!!).
I know but the mark scheme gives -1= 4sin pi/6 times t
However sin pi/6 = 1/2 which means t should equal to -1/2 but the markscheme says t= -0.482
5. (Original post by BBeyond)
June 12 4b what a horrible q such retarded angles
Haha yeh no nice numbers but still resulted in a nice k.

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6. (Original post by JustDynamite)
I know but the mark scheme gives -1= 4sin pi/6 times t
However sin pi/6 = 1/2 which means t should equal to -1/2 but the markscheme says t= -0.482
sin(pi/6 x t) not sin(pi/6) xt
7. (Original post by samb1234)
You can do it with a hemisphere of radius r+delta r - one of radius r but it's ugly
Ah yes that should do it.

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8. (Original post by physicsmaths)
Haha yeh no nice numbers but still resulted in a nice k.

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Yh true I had to do it two ways to check tho seemed dodgy to me. Did u do moments or recalc c.o.m?

(Original post by samb1234)
It's a throwback to m2 which is a severe problem for me as i was pretty **** at them at the time and that was a year ago...
Ahahah doing m2 this year so I've got that to look forward to
9. (Original post by BBeyond)
Yh true I had to do it two ways to check tho seemed dodgy to me. Did u do moments or recalc c.o.m?

Ahahah doing m2 this year so I've got that to look forward to
I actually got one in my exam but luckily had done so much practice that i was just about able to get through it
10. (Original post by BBeyond)
Yh true I had to do it two ways to check tho seemed dodgy to me. Did u do moments or recalc c.o.m?

Ahahah doing m2 this year so I've got that to look forward to
i did moments
11. (Original post by physicsmaths)
i did moments
Recalculating the COM is so much cleaner. If you use the tan addition formula then you don't even need a calculator (and therefore I've found it the marginally more useful thing for step, but ymmv)
12. (Original post by Krollo)
Recalculating the COM is so much cleaner. If you use the tan addition formula then you don't even need a calculator (and therefore I've found it the marginally more useful thing for step, but ymmv)
It seems like it is cleaner yes. I did the instinct which is normally moments and worked first try so I didn't bother anything else. Yeh actually the tan addition formula cleans it up quite nicely. Well played lad, well played.

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13. hmm anyone done M3 Jan 16 (no spoilers to follow)? My friend asked about a method about q7 earlier and it makes sense to me but isnt covered on the markscheme. Could anyone verify this?
14. (Original post by EnglishMuon)
hmm anyone done M3 Jan 16 (no spoilers to follow)? My friend asked about a method about q7 earlier and it makes sense to me but isnt covered on the markscheme. Could anyone verify this?
That was the paper I sat, Q7 seemed like a normal typical circular motions question.
15. (Original post by Zacken)
That was the paper I sat, Q7 seemed like a normal typical circular motions question.
ah nice. Yea it seems the same to me but
Spoiler:
Show
they noticed the second part before doing the first where they had to show u>... so they tried to save time by looking at the tension in the rod (or whatever it was). They argued that the at the top of the circle. If this holds, it implies which satisfies the criteria in the question. Im not 100% sure they can say T>0 at the top unlike the situation with the reaction force and a particle rolling on a larger sphere but idk.
16. When calculating moments, do the forces have to be perpendicular to the length of the rod?
17. (Original post by Krollo)
Recalculating the COM is so much cleaner. If you use the tan addition formula then you don't even need a calculator (and therefore I've found it the marginally more useful thing for step, but ymmv)
It seems like it is cleaner yes. I did the instinct which is normally moments and worked first try so I didn't bother anything else. Yeh actually the tan addition formula cleans it up quite nicely. Well played lad, well played.

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18. (Original post by EnglishMuon)
ah nice. Yea it seems the same to me but
Spoiler:
Show
they noticed the second part before doing the first where they had to show u>... so they tried to save time by looking at the tension in the rod (or whatever it was). They argued that the at the top of the circle. If this holds, it implies which satisfies the criteria in the question. Im not 100% sure they can say T>0 at the top unlike the situation with the reaction force and a particle rolling on a larger sphere but idk.
Spoiler:
Show
I think they are confusing the criterion for complete circles.

Strings - tension at top > 0.

Rods - speed at top > 0.

This makes intuitive sense since rods cannot exactly go slack or anything, can they - so the condition is that the rod must have a velocity at the top for it to perform complete circles whereas strings can go slack so the condition is that tension at the top needs to be greater than 0.
19. (Original post by physicsmaths)
It seems like it is cleaner yes. I did the instinct which is normally moments and worked first try so I didn't bother anything else. Yeh actually the tan addition formula cleans it up quite nicely. Well played lad, well played.

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Ty bro.
20. Anyone know if Arsey does M3 model answers?

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