Hey there! Sign in to join this conversationNew here? Join for free
x Turn on thread page Beta
    • Thread Starter
    Offline

    7
    ReputationRep:
    Hi,

    I remember doing this type of question for GCSE additional maths but I completely forgot how to do it.

    1. A uniform rod AB of length 12a and weight 4W is suspended by strings attached at C and D, where AC=3a and BD=4a. The breaking strain of the string at C is 3W and that at D is 3.8W. An object of weight W is attached to the beam at a distance x from A. Find the range of values of x if neither string is to break.

    I've drawin the correct diagram I think. I've put 3W and 3.8W as T that acts upwards and the 4Wg as downward force.

    I tried balancing the forces together so like:

    (Wgx)+(4Wg x 6a)=(3W x 3a) + (3.8W + 8a)

    and then I tried to solve x. But I'm getting the wrong answer?
    and how would I obtain 2 values of x to make a range?

    Thanks for your help
    Offline

    14
    ReputationRep:
    (Original post by liemluji)
    Hi,

    I remember doing this type of question for GCSE additional maths but I completely forgot how to do it.

    1. A uniform rod AB of length 12a and weight 4W is suspended by strings attached at C and D, where AC=3a and BD=4a. The breaking strain of the string at C is 3W and that at D is 3.8W. An object of weight W is attached to the beam at a distance x from A. Find the range of values of x if neither string is to break.

    I've drawin the correct diagram I think. I've put 3W and 3.8W as T that acts upwards and the 4Wg as downward force.

    I tried balancing the forces together so like:

    (Wgx)+(4Wg x 6a)=(3W x 3a) + (3.8W + 8a)

    and then I tried to solve x. But I'm getting the wrong answer?
    and how would I obtain 2 values of x to make a range?

    Thanks for your help
    Start with the tensions as variables, Tc and Td.

    Taking moments about C will give you an equation involving Td but not Tc. Get Td on its own from this equation and then say that Td < 3.8W. Solve that as an inequality for x.

    Repeat by taking moments about D.
    • Community Assistant
    Online

    20
    ReputationRep:
    Community Assistant
    (Original post by liemluji)
    Hi,

    I remember doing this type of question for GCSE additional maths but I completely forgot how to do it.

    1. A uniform rod AB of length 12a and weight 4W is suspended by strings attached at C and D, where AC=3a and BD=4a. The breaking strain of the string at C is 3W and that at D is 3.8W. An object of weight W is attached to the beam at a distance x from A. Find the range of values of x if neither string is to break.

    I've drawin the correct diagram I think. I've put 3W and 3.8W as T that acts upwards and the 4Wg as downward force.

    I tried balancing the forces together so like:

    (Wgx)+(4Wg x 6a)=(3W x 3a) + (3.8W + 8a)

    and then I tried to solve x. But I'm getting the wrong answer?
    and how would I obtain 2 values of x to make a range?

    Thanks for your help
    Can you post your diagram?
    • Thread Starter
    Offline

    7
    ReputationRep:
    (Original post by tiny hobbit)
    Start with the tensions as variables, Tc and Td.

    Taking moments about C will give you an equation involving Td but not Tc. Get Td on its own from this equation and then say that Td < 3.8W. Solve that as an inequality for x.

    Repeat by taking moments about D.
    So we don't take the added weight W into calculating moment about C?

    (Td x 5a) - (4Wg x 3a) < 3.8W
    or
    (Td x 5a)- (4Wg x 3a) - (Wg x 'x' <3.8W?

    I still cant get the answer. Do you mind helping me more :'(

    --> NVM I got the answer thanks for your help!
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: September 6, 2016
Poll
Do I go to The Streets tomorrow night?
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.