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# Rotational Mechanics watch

1. (Original post by TeeEm)
put up a solution and will check it
Not tried it just yet, but I will do later. It's just that the last line 'in terms of m and g' bothered me. Would there not have to be another length in there somewhere?
2. (Original post by A Slice of Pi)
Not tried it just yet, but I will do later
yes there is a typo ... I checked in my written solution and I have 4/3 mga
3. (Original post by TeeEm)
yes there is a typo ... I checked in my written solution and I have 4/3 mga
I get this also
Attached Images
4. sol1.pdf (466.0 KB, 89 views)
5. (Original post by A Slice of Pi)
I get this also

your mechanics is too good ...
here is my solution
Attached Images

6. (Original post by TeeEm)

your mechanics is too good ...
here is my solution
Neat and nice
thank you
7. (Original post by depymak)
Neat and nice
thank you
mine is supposed to be neat and nice....
"A Slice of Pi" is not ....
8. (Original post by TeeEm)
mine is supposed to be neat and nice....
"A Slice of Pi" is not ....
I meant yours (TeeEm)
9. (Original post by TeeEm)
we have to wait for the Mechanics master-kid .
(Hopefully I catch him !!!, as he looks unbeatable at the moment)

I get 4/3 mg (I could be wrong)
You are probably right. I misread your question - I thought that it said that there was a couple acting contrary to the torque generated by the falling mass - in fact, it's a frictional couple, so it can't be analysed the way I was going about it - you need an energy argument. (I also used h instead of 2h when calculating the final speed of the falling mass but that's trivial). I'll have to start taking more care with these questions.
10. (Original post by atsruser)
You are probably right. I misread your question - I thought that it said that there was a couple acting contrary to the torque generated by the falling mass - in fact, it's a frictional couple, so it can't be analysed the way I was going about it - you need an energy argument. (I also used h instead of 2h when calculating the final speed of the falling mass but that's trivial). I'll have to start taking more care with these questions.
I am giving up ...
A slice of pi made mince meat of this one too ...
11. (Original post by TeeEm)
I am giving up ...
Err, why? Confused.
12. (Original post by atsruser)
Err, why? Confused.
this A level kid does everything I throw at him ...
polars, intrinsic, rotations, variable mass ....
13. (Original post by TeeEm)
this A level kid does everything I throw at him ...
polars, intrinsic, rotations, variable mass ....
But why is that a bad thing?
14. (Original post by A Slice of Pi)
By why is that a bad thing?
I am very busy in the next 2 days but I am making a question with a marble rotating inside a cone and moving up and down ....
Start revising ...
15. (Original post by TeeEm)
I am very busy in the next 2 days but I am making a question with a marble rotating inside a cone and moving up and down ....
Start revising ...
Fair enough, but as long as its next week because I'm not going to be able to do any maths this weekend as I have a fair bit of chemistry work to do...
16. (Original post by TeeEm)
this A level kid does everything I throw at him ...
polars, intrinsic, rotations, variable mass ....
I'm taking your questions too casually - trying to do them on scraps of paper while doing other stuff. I'm going to up my game from now on.
17. (Original post by atsruser)
I'm taking your questions too casually - trying to do them on scraps of paper while doing other stuff. I'm going to up my game from now on.
18. (Original post by TeeEm)
When it comes to me and your mechanics questions, Mr TeeEm, from now on, it's no more Mister Nice Guy.
19. (Original post by TeeEm)
this A level kid does everything I throw at him ...
polars, intrinsic, rotations, variable mass ....
Pi is an A-level kid?

Puts me to shame...

Spoiler:
Show
At least I don't have to do Chemistry
20. (Original post by Mathemagicien)
Pi is an A-level kid?

Puts me to shame...
Spoiler:
Show
At least I don't have to do Chemistry
so (s)he claims
21. (Original post by atsruser)
Am I being stupid?

Spoiler:
Show
The mass has lost of PE when it comes to rest, which can only be converted into the work against the couple. This turns through so
Given someone has repped this, I ought to point out that the argument is wrong (I forgot about the jerk => inelastic) - you can see the correct approach further down the thread. (Conservation of AM to start with, which is always true, so we don't have to worry about elastic/inelastic processes).

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