The Student Room Group

M3: COM

for part b,

I did the COM of the solid = the the COM of the stud, but this isn't right. how come?
bump
https://aectutors.co.uk/wpdm-package/edexcel-maths-m3-pdf/?wpdmdl=9543

this type of question (hanging mass with mass attached) isnt in the textbook.
Original post by Maths&physics
bump


Your diagram is not quite correct.

You get λ\lambda from taking moments about BB. Hence we have:

(4+k)mgd1=λmgd2(4+k)mg \cdot d_1 = \lambda m g \cdot d_2,

where you know kk and can determine d1,d2d_1, d_2 fairly easy.

For d2d_2 I suggest you have a look at the second image and notice that d1+d2=2rsin60d_1 + d_2 = 2r \sin 60.



(edited 5 years ago)
Original post by RDKGames
Your diagram is not quite correct.

You get λ\lambda from taking moments about BB. Hence we have:

(4+k)mgd1=λmgd2(4+k)mg \cdot d_1 = \lambda m g \cdot d_2,

where you know kk and can determine d1,d2d_1, d_2 fairly easy.

For d2d_2 I suggest you have a look at the second image and notice that d1+d2=2rsin60d_1 + d_2 = 2r \sin 60.





thanks.

so we need to find the perpendicular distance from the COM to the line of action and not the other way around? but the mass is a point and not a line....?
(edited 5 years ago)
Very odd questions...

Original post by Maths&physics
thanks.

so we need to find the perpendicular distance from the COM to the line of action and not the other way around?

Obviously the perp. distance will be the same between the two things regardless from which you begin measuring...?

but the mass is a point and not a line....?


Yes mass is concentrated onto a single point in these models... where you are getting the impression that mass is 'a line' ... ?
Original post by RDKGames
Very odd questions...


Obviously the perp. distance will be the same between the two things regardless from which you begin measuring...?



Yes mass is concentrated onto a single point in these models... where you are getting the impression that mass is 'a line' ... ?


brilliant!! thanks

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