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

    8
    ReputationRep:
    Name:  m2.PNG
Views: 5
Size:  82.2 KBAttachment 702158
    Stuck on past paper question would really appreicate some help, ive done the first part but am stuck on the second bit, the mark scheme is saying to take moments about A but in the mark scheme the perpendicular distance is root2xa which is the distance to O not A so im confused
    Offline

    9
    ReputationRep:
    it would help if you gave a link to which past paper and question you are actually stuck on?
    • Thread Starter
    Offline

    8
    ReputationRep:
    (Original post by _RobbieL_)
    it would help if you gave a link to which past paper and question you are actually stuck on?
    sorry the pic didnt send first time
    • Community Assistant
    • Welcome Squad
    Online

    20
    ReputationRep:
    (Original post by uchihaitachi0023)
    ...
    When it is hanged from A, you have two forces acting directly downwards; the CoM of the lamina, and the particle at D. You are told that OA is vertical, so I here extended the direction of the force backwards for you and so when you are taking the moments about A, you want the length of the red line as it's perpendicular to the direction of the force. Upon basic inspection, you should find that the red line is the same length as OD. And OD is just length a\sqrt{2}. Get it?

    • Thread Starter
    Offline

    8
    ReputationRep:
    (Original post by RDKGames)
    When it is hanged from A, you have two forces acting directly downwards; the CoM of the lamina, and the particle at D. You are told that OA is vertical, so I here extended the direction of the force backwards for you and so when you are taking the moments about A, you want the length of the red line as it's perpendicular to the direction of the force. Upon basic inspection, you should find that the red line is the same length as OD. And OD is just length a\sqrt{2}. Get it?

    goddamn cant believe i didnt see that, nice one mate saved me a lot of time
    • Thread Starter
    Offline

    8
    ReputationRep:
    (Original post by RDKGames)
    When it is hanged from A, you have two forces acting directly downwards; the CoM of the lamina, and the particle at D. You are told that OA is vertical, so I here extended the direction of the force backwards for you and so when you are taking the moments about A, you want the length of the red line as it's perpendicular to the direction of the force. Upon basic inspection, you should find that the red line is the same length as OD. And OD is just length a\sqrt{2}. Get it?

    i know its a big ask but could u draw on diagram again to show how the centre of mass would be perpendicular to A,im having trouble visualising it
    • Community Assistant
    • Welcome Squad
    Online

    20
    ReputationRep:
    (Original post by uchihaitachi0023)
    i know its a big ask but could u draw on diagram again to show how the centre of mass would be perpendicular to A,im having trouble visualising it
    You want to find the red line. You know the pink line's length. The angle between the pink and the black line is...?? Hence then use cosine to work out the red line.
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    What newspaper do you read/prefer?
    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
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • 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

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