Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    0
    ReputationRep:
    Find the area of the part of the plane x+y+z=1 which lies in the first octant.

    This I managed to do correctly - root 3/2 - which I found by projecting the area onto the x-y plane.. (though I'm getting a minus sign which im not sure about...when i project it onto x-y i see that it is the double integral of root 3 where the line is basically y= -x +1 -- any ideas why?)

    It then asks to find its centre of mass using integration..

    How would I do this?
    THanks
    • Thread Starter
    Offline

    0
    ReputationRep:
    anyone?
    Offline

    3
    ReputationRep:
    On the face of it, King, this is an odd question. When you posted it earlier, it was pointed out that you had an equilateral triangle and so it was obvious both what the area was and also where the centre of mass was. It doesn't need double integrals.

    May I ask where the question comes from?
    • Thread Starter
    Offline

    0
    ReputationRep:
    ahh okay fine..

    so its COM is 1/3, 1/3, 1/3 ?

    thanks

    it is from a double integral problem sheet
    Offline

    3
    ReputationRep:
    I think the centroid is (1/3, 1/3, 1/3).

    Perhaps they're asking you to practice transforming variables and working out limits in cases that are easy to check by other methods.
    Offline

    3
    ReputationRep:
    In which case I assume you're OK with centre-of-mass = first moment of area / area, which I imagine converts into some neat double-integral recipe.
 
 
 
Poll
Do you agree with the PM's proposal to cut tuition fees for some courses?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.