Advertisement
If you have a new account but are having problems posting or verifying your account, please email us on hello@boards.ie for help. Thanks :)
Hello all! Please ensure that you are posting a new thread or question in the appropriate forum. The Feedback forum is overwhelmed with questions that are having to be moved elsewhere. If you need help to verify your account contact hello@boards.ie
Hi there,
There is an issue with role permissions that is being worked on at the moment.
If you are having trouble with access or permissions on regional forums please post here to get access: https://www.boards.ie/discussion/2058365403/you-do-not-have-permission-for-that#latest

Quick question on reducing a moment and force to a single force

  • 09-12-2010 2:51pm
    #1
    Ste234
    Registered Users, Registered Users 2 Posts: 65 ✭✭


    The question I'm doing asks me to reduce a moment and force at point a to a single force system. Is this just basically d=M/F so that d is the distance from a that the single force, F is. Where M is the moment.

    So if I have a moment of 640Nm and a force of 60i + 20j N at A,
    would the single force system just be a distance from A so that d=640/F
    We're not given a specific distance though.


Comments

  • #2
    Morbert
    Registered Users, Registered Users 2 Posts: 3,457 ✭✭✭Morbert


    Ste234 wrote: »
    The question I'm doing asks me to reduce a moment and force at point a to a single force system. Is this just basically d=M/F so that d is the distance from a that the single force, F is. Where M is the moment.

    So if I have a moment of 640Nm and a force of 60i + 20j N at A,
    would the single force system just be a distance from A so that d=640/F
    We're not given a specific distance though.

    I'm not sure what you mean. Is the force 60i+20j inducing the moment? If it is then I would imagine it's already a single force system.


  • #3
    Ste234
    Registered Users, Registered Users 2 Posts: 65 ✭✭Ste234


    part (ii) is the question?


  • #4
    Morbert
    Registered Users, Registered Users 2 Posts: 3,457 ✭✭✭Morbert


    Hmm... This looks like a tough one. I am not sure of the solution, by my logic would be something like this.

    (1) Represent the couple as two forces (each of magnitude 46.666j...) on either end of the beam.

    (2) Resolve the forces on the two end so get two forces (6.666...j on the left, 60i + 13.3333...j on the right)

    (Answer) This is equivalent to a couple at the centre of 40 Nm (i.e. 3*6.666... + (-3*-6.666...) ) and a force at the right of magnitude 60i + 20j

    [edit]-fixed mistake


  • #5
    FISMA
    Closed Accounts Posts: 2,616 ✭✭✭FISMA


    What is the 280mN a resistive or resultant torque? I am guessing that it's the sum of the torques = (moment of inertia)*(angular acceleration). The moment of inertia in this case being (1/12 * ML^2)

    Sorry if I totally missed the boat on this, it has been a while since Mechanics. Also, I don't use the term couples that often any more. I cannot remember seeing it in many modern texts.

    A couple causes rotation, but not translation, correct? I will proceed using what I think they're trying to say - their usage of a couple, like this.
    steeringwheel.gif
    The 40j N force causes pure rotation about the pivot, no translation.

    The 60i + 60j N Force causes both translation and rotation.

    Part (i)
    It looks as if they want you to break up the Force on the RHS into it's two components. Since the angle of that Force is 45 degrees, they're being somewhat nice:-)

    I really don't like the way they worded this problem...

    I think that's all they want you to do - resolve that Force on the RHS into it's component in the y direction.

    Part (ii)
    You have to add the two Forces.

    I would be tempted to add the RH Force to the LH Force. You already have your angle, and the adjacent - 40jN. You'll then want where it hits the beam - the opposite, looks like we want the tan of theta.

    If I totally missed the boat on the problem and oversimplified it, sorry :o!



Advertisement