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Weight distribution on a tilted object

  • 08-08-2008 1:51am
    #1
    BrokenArrows
    Registered Users, Registered Users 2 Posts: 7,516 ✭✭✭


    Here is something that just poped into my head. Dont ask me why!

    Say you have a block weighing 1 tonne. It is being lifted from one end so that it is at lets say 20degree angle.

    How much of the total weight is baring down on the lifter v's the ground.

    A = Ground
    B = Lifter

    weightdist.jpg

    edit: the block shall be totally cubed. nevermind the drawing :D


Comments

  • #2
    MathsManiac
    Registered Users, Registered Users 2 Posts: 1,595 ✭✭✭MathsManiac


    Leaving cert applied maths (statics) will sort this out.

    Let the force upwards at B be T. Let the force applied by the ground to the block (i.e. the reaction) be R. Let the length of the diagonal of the visible square face of the block be 2L. Note that the weight of the block acts downwards through its centre of gravity. Let A be the angle of tilt (20 degrees if you like). Draw a force diagram, and you get, (I think):

    Forces up = forces down => R+T=1000g
    Total moments about the centre of gravity = 0 => RLsin(45-A) = TLsin(45+A)

    Cancel L in the second equation and then solve the two equations to find the two unknowns R and T.


  • #3
    BrokenArrows
    Registered Users, Registered Users 2 Posts: 7,516 ✭✭✭BrokenArrows


    sorry you have totally lost me.


  • #4
    Michael Collins
    Moderators, Science, Health & Environment Moderators Posts: 1,852 Mod ✭✭✭✭Michael Collins


    BrokenArrows wrote: »
    sorry you have totally lost me.

    Well you do need to understand some basics of forces to get the answer like!

    Where did this come from out of curiosity? Lifting a TV up a stairs :) ?


  • #5
    LeixlipRed
    Closed Accounts Posts: 6,081 ✭✭✭LeixlipRed


    That's a pretty heavy TV. Perhaps some sort of medium sized cube shaped rhino??


  • #6
    Michael Collins
    Moderators, Science, Health & Environment Moderators Posts: 1,852 Mod ✭✭✭✭Michael Collins


    LeixlipRed wrote: »
    That's a pretty heavy TV. Perhaps some sort of medium sized cube shaped rhino??

    Last time I lifted a CRT TV up a stairs I'd swear it weighed a tonne!


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  • #7
    BrokenArrows
    Registered Users, Registered Users 2 Posts: 7,516 ✭✭✭BrokenArrows


    was watching some rubbish on TV. some guy lifting a car that had some weight written on it. Just wondering how much roughly he would be lifting seen as alot of it is still resting on the ground.

    yes i know car is not perfectly square etc.


  • #8
    MathsManiac
    Registered Users, Registered Users 2 Posts: 1,595 ✭✭✭MathsManiac


    Been away.

    To answer your last question: to get his end to leave the ground, he must apply a force of just over half the weight of the car. The farther he tilts it, the more the weight shifts to A and the less force he needs at B.


  • #9
    alan4cult
    Registered Users, Registered Users 2 Posts: 1,583 ✭✭✭alan4cult


    Michael Collins wrote: »
    Where did this come from out of curiosity? Lifting a TV up a stairs :) ?
    ROFL


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