Turn on thread page Beta
    • Thread Starter
    Offline

    17
    ReputationRep:


    I have done part a already. Here's the MS



    All I want to know, for part B, is why have they done T2 - T1. Surely it would be T1-T2 for the resultant force? Since the particle will move in the direction of T1 when let go. Thanks.
    Offline

    18
    ReputationRep:
    I think it doesn't make a difference which they use, it just changes the sign on the fraction in the first half of the second line.
    • Thread Starter
    Offline

    17
    ReputationRep:
    It does change the sign. I get a positive whereas they get a -ve. If you dont get a negative sign in this, then you havent proved SHM. So, I need to know why they used T2-T1 instead of vice versa.
    Offline

    15
    ReputationRep:
    T2-T1 = -(T1-T2). It shouldn't make a difference to the presence of SHM.
    • Thread Starter
    Offline

    17
    ReputationRep:
    (Original post by marcusmerehay)
    T2-T1 = -(T1-T2). It shouldn't make a difference to the presence of SHM.
    But that -ve sign is vital. The formula for SHM is:

     a = -w^2 x

    If I don't have that -ve sign, how am I supposed to show SHM?
    Offline

    11
    ReputationRep:
    (Original post by 2710)
    But that -ve sign is vital. The formula for SHM is:



    If I don't have that -ve sign, how am I supposed to show SHM?
    Initially, you're measuring the displacement from equilibrium, x, from left to right (because it starts to the right of the equilibrium point). Thus, as the net restoring force acting upon the mass is directed toward the left (toward the equilibrium point), you state that the force is the negative of the mass times the acceleration. This means you have -(T1 - T2) = T2 - T1.

    It's not 'proof' in the nice sense of the word, but looking at the solutions you've provided, I can't think of a better answer.
    Offline

    11
    ReputationRep:
    (Original post by 2710)
    But that -ve sign is vital. The formula for SHM is:

     a = -w^2 x

    If I don't have that -ve sign, how am I supposed to show SHM?
    it will be
    (T1-T2)=-ma
    the -ma specify the particle is accelerating in the opposite direction towrds the centre

    multiply through by -1 you get
    -T1+T2=ma
    • Thread Starter
    Offline

    17
    ReputationRep:
    (Original post by james.h)
    Initially, you're measuring the displacement from equilibrium, x, from left to right (because it starts to the right of the equilibrium point). Thus, as the net restoring force acting upon the mass is directed toward the left (toward the equilibrium point), you state that the force is the negative of the mass times the acceleration. This means you have -(T1 - T2) = T2 - T1.

    It's not 'proof' in the nice sense of the word, but looking at the solutions you've provided, I can't think of a better answer.
    Ah I get it. SO either the force of the displacement has to be -ve/+ve, because if they were the same it would imply that they are in the same direction, when the force is actually moving in the opposite direction. Amirite?

    Thanks
    Offline

    18
    ReputationRep:
    (Original post by 2710)
    All I want to know, for part B, is why have they done T2 - T1. Surely it would be T1-T2 for the resultant force? Since the particle will move in the direction of T1 when let go. Thanks.
    Look at the direction in which you are measuring 'x'.

    T2 acts in the same direction, so its contribution to \ddot{x} is positive.
    T1 acts in the opposite direction, so its contribution to \ddot{x} is negative.
    Offline

    11
    ReputationRep:
    No problem.
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: January 21, 2010
The home of Results and Clearing

1,901

people online now

1,567,000

students helped last year

University open days

  1. SAE Institute
    Animation, Audio, Film, Games, Music, Business, Web Further education
    Thu, 16 Aug '18
  2. Bournemouth University
    Clearing Open Day Undergraduate
    Fri, 17 Aug '18
  3. University of Bolton
    Undergraduate Open Day Undergraduate
    Fri, 17 Aug '18
Poll
Do you want your parents to be with you when you collect your A-level results?
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.