The Student Room Group
Competition - post a photo you've taken of nature >>
Competition - post a photo you've taken of nature >>
Competition - post a photo you've taken of nature >>

m2- question about a governor

I'm doing question 10.

I don't know what a governor is and I've made assumptions that could well be rubbish. My answer is almost correct but I need some guidance.

my answer is 0.75w^2 - 2gRoot3 instead of 0.75w^2 - gRoot3. I've been looking where I could have a Root3 too many and I've marked them on my answer. I am assuming that the thing called C is hovering and is not supported by anything so the 6kg counts as a downward force. Perhaps it doesn't. Perhaps that's what happens on the point of moving up - I haven't done part b yet.

I think I'd like someone to explain what's going on at A when C hasn't started to move up.

Thanks
Scan0014.pdf374.6KB
Scan0015.pdf357.9KB
Reply 1
Avatar for TeeEm
TeeEm
19
Original post by maggiehodgson
I'm doing question 10.

I don't know what a governor is and I've made assumptions that could well be rubbish. My answer is almost correct but I need some guidance.

my answer is 0.75w^2 - 2gRoot3 instead of 0.75w^2 - gRoot3. I've been looking where I could have a Root3 too many and I've marked them on my answer. I am assuming that the thing called C is hovering and is not supported by anything so the 6kg counts as a downward force. Perhaps it doesn't. Perhaps that's what happens on the point of moving up - I haven't done part b yet.

I think I'd like someone to explain what's going on at A when C hasn't started to move up.

Thanks


it gets to move up when the vertical component of the tension in the upper half is greater than the downward component of the tensions in the lower section plus the weight
Original post by TeeEm
it gets to move up when the vertical component of the tension in the upper half is greater than the downward component of the tensions in the lower section plus the weight


Thanks, I'd sort of thought that for the next bit but I still don't know where my extra groot3 is coming from. Any thoughts on that?
Reply 3
Avatar for TeeEm
TeeEm
19
Original post by maggiehodgson
Thanks, I'd sort of thought that for the next bit but I still don't know where my extra groot3 is coming from. Any thoughts on that?


I would need to do the workings myself

try again

I will attempt the question before the next hour and i will post some help if no one else does
Original post by maggiehodgson
...


I'm not clear what your first equation is meant to represent.

If you're resolving vertically for P (or Q), then there is no "+6g", nor do you need to double everything. The only forces acting at P,Q are T1, 3g, and T2.

I would work with just one of the masses, rather than try and combine both P,Q into one equation straight off.

Of course later on there are two rods connecting to the 6kg mass, symmetrically, and at that stage you would double up appropriately.
(edited 9 years ago)
Original post by TeeEm
I would need to do the workings myself

try again

I will attempt the question before the next hour and i will post some help if no one else does



Looking forward to hearing from you.
Reply 6
Avatar for TeeEm
TeeEm
19
Original post by maggiehodgson
Looking forward to hearing from you.


I have an answer (I hope I did not do it too quickly) of w^2=28g/3

is this anywhere close?
Original post by ghostwalker
I'm not clear what your first equation is meant to represent.

If you're resolving vertically for P (or Q), then there is no "6g", nor do you need to double everything.

I would work with just one of the masses, rather than try and combine both P,Q into one equation straight off.

Of course later on there are two rods connecting to the 6kg mass, symmetrically, and at that stage you would double up appropriately.



Yes I was resolving vertically and I thought that the collar, C, would be pulling down. Are you saying that in the first position we don't use 6kg it's sitting on something?

If I ignored the 6g then I can see that there would be no need to double up on the other parts.

In part b) the 6kg now comes into play so I do need to double up. So what I've actually done is the start of part b?

Thanks
Original post by maggiehodgson
Yes I was resolving vertically and I thought that the collar, C, would be pulling down. Are you saying that in the first position we don't use 6kg it's sitting on something?

If I ignored the 6g then I can see that there would be no need to double up on the other parts.


When considering P,Q, the 6kg mass does not come into it. It's not a force acting on P, or Q, directly. Doesn't matter whether the 6kg mass is sitting on something or not. It's T2 that's acting on P,Q.


In part b) the 6kg now comes into play so I do need to double up. So what I've actually done is the start of part b?

Thanks


(Edit: I wouldn't use it as such. It's as if you've amalgamated a couple of equations into one at the outset.)

At this stage you can resolve forces at C, and here you create a link between the T2's and the 6kg mass.
(edited 9 years ago)
Reply 9
Avatar for TeeEm
TeeEm
19
Original post by TeeEm
I have an answer (I hope I did not do it too quickly) of w^2=28g/3

is this anywhere close?


correction I did not read properly

I got these answers

if bottom mass is in contact tension is 3/4w^2-g times root 3

it lifts if w^2> 4groot3
Original post by ghostwalker
When considering P,Q, the 6kg mass does not come into it. It's not a force acting on P, or Q, directly. Doesn't matter whether the 6kg mass is sitting on something or not. It's T2 that's acting on P,Q.



(Edit: I wouldn't use it as such. It's as if you've amalgamated a couple of equations into one at the outset.)

At this stage you can resolve forces at C, and here you create a link between the T2's and the 6kg mass.



So my first line is this

T2 cos30 + 3g = T1 cos30.

At this point my thoughts are bobbing about. If the 6kg isn't doing anything, what's it there for?
Original post by TeeEm
I have an answer (I hope I did not do it too quickly) of w^2=28g/3

is this anywhere close?



The question was to find the tension in the lower rods in terms of the angular speed. So I don't think that your result is what we're looking for. It might well be true, of course.

If I get that far, I'll let you know.
Original post by maggiehodgson
So my first line is this

T2 cos30 + 3g = T1 cos30.

At this point my thoughts are bobbing about. If the 6kg isn't doing anything, what's it there for?


In part a)

As long as T2 is insufficient to lift the 6kg mass, it's holding the governor in shape, so your radius at P remains fixed. It's also allowing you to have a T2.

As long as C is not moving, the situation is no different to C being fixed at A.

Edit: You don't need to consider the 6kg mass for part a), as I said, it's not acting on P or Q.
(edited 9 years ago)
Reply 13
Avatar for TeeEm
TeeEm
19
Original post by maggiehodgson
The question was to find the tension in the lower rods in terms of the angular speed. So I don't think that your result is what we're looking for. It might well be true, of course.

If I get that far, I'll let you know.


you need to look at my latest post.Quote me if these are your answers for a and b...
Original post by ghostwalker
In part a)

As long as T2 is insufficient to lift the 6kg mass, it's holding the governor in shape, so your radius at P remains fixed. It's also allowing you to have a T2.

As long as C is not moving, the situation is no different to C being fixed at A.

Edit: You don't need to consider the 6kg mass for part a), as I said, it's not acting on P or Q.



My head needs to think on this. Will come back.
Reply 15
Avatar for TeeEm
TeeEm
19
Original post by TeeEm


I got these answers

if bottom mass is in contact, tension is 3/4w^2-g times root 3

it lifts if w^2> 4groot3



look at the PDF.

m2_m3_circular_motion.pdf


This is a similar scenario in terms of constants

Not quite your question but see if this helps.

[PS I am guessing you are on an engineering course of some kind. I hope you do not get confused with the radial acceleration outwards. In mathematics we mark radial acceleration in the direction of r increasing i.e outwards, but its value is -w2r, so it works the same...]
Original post by maggiehodgson
My head needs to think on this. Will come back.


Another thought that may help.

As long as tension in the lower strutt is insufficient to lift C, what would happen if you change the mass at C to 60kg, say. Does it effect the tension in T2?
Original post by TeeEm
look at the PDF.

m2_m3_circular_motion.pdf


This is a similar scenario in terms of constants

Not quite your question but see if this helps.

[PS I am guessing you are on an engineering course of some kind. I hope you do not get confused with the radial acceleration outwards. In mathematics we mark radial acceleration in the direction of r increasing i.e outwards, but its value is -w2r, so it works the same...]


Well, thank you SOOOO much for the pdf. Although it's nothing different from what Ghostwalker has been saying to me somehow today it clicked. What a relief.

No, I'm not on an engineering course. I'm doing M2 for no reason at all other than curiosity and fun. No exams to sit - until my masochistic streak kicks in. No further studies in mind except perhaps A2 Further Maths. Just something to do that gives me a buzz.

Thank you for your input.
Original post by ghostwalker
Another thought that may help.

As long as tension in the lower strutt is insufficient to lift C, what would happen if you change the mass at C to 60kg, say. Does it effect the tension in T2?



Hi.

With a sleep, what you said yesterday that I could not see, today makes perfect sense. I looked at the pdf from the other poster and as soon as I read it I knew that I'd got it already.

I'll have a go at part b now.

Many thanks for all your efforts - I really appreciate them.
Reply 19
Avatar for TeeEm
TeeEm
19
Original post by maggiehodgson
Well, thank you SOOOO much for the pdf. Although it's nothing different from what Ghostwalker has been saying to me somehow today it clicked. What a relief.

No, I'm not on an engineering course. I'm doing M2 for no reason at all other than curiosity and fun. No exams to sit - until my masochistic streak kicks in. No further studies in mind except perhaps A2 Further Maths. Just something to do that gives me a buzz.

Thank you for your input.


All good. Always a pleasure.

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you