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Calculating force to accelerate object

  1. Mar 23, 2010 #1
    1. The problem statement, all variables and given/known data

    What is the initial force P required to accelerate the table upwards at 0.3ms^2.



    2. Relevant equations

    I have attached the the problem, it is drawn out in paint. The mass expected to be carried on the table is 200kg and can be assumed to be a point mass acting at the position shown on the diagram. Assuming that the table moves vertically and does not rotate under the force P, I need to find what value it initially must be so that it causes an initial acceleration of 0.3ms^2 upwards.


    3. The attempt at a solution

    I have tried for a day to work this out and I am not getting anywhere! any help would be very much appreciated.
     

    Attached Files:

  2. jcsd
  3. Mar 23, 2010 #2
    mechanics help, finding force

    Hi, I am struggling on this problem- I have attached it as a jpg as this makes it most clear.


    Problem is essentially you have a table that rises and lowers itself using an actuator. I need to calculate the force needed at the initial conditions as illustrated in the attachment that would allow the table to rise at an initial acceleration of 0.3m^2.

    Would anyone be able to help me solve this, i've been working on it for days....
     

    Attached Files:

  4. Mar 23, 2010 #3
    Re: mechanics help, finding force

    Try finding all the static forces in the members, and reaction forces first. This will determine the masses. Use kinematics to find the acceleration at the point load using a known acceleration direction (maybe assume the 200kg mass travels vertical only). Thats my suggestion
     
  5. Mar 24, 2010 #4
    Hi.
    I'm not an expert so beware, but:

    Am I reading this diagram correctly? If I look at the right angled triangle whose three sides are:

    1) Left hand attachment to table to right hand table leg 0.67m +0.77m

    2) Vertical distance right hand table leg to table surface

    3) Horizontal distance along table from LH attachment to intersection with 2


    Then I get the table height as only (0.67m +0.77m)sin7deg 17.5cm

    More importantly (0.67m +0.77m)cos7deg is 1.43m but the diagram shows this to be the distance from LH attachment to mass of 200kg implying the mass is vertically above the right hand table leg although the diagram doesn't show that.

    My suggestion is to assume the system is in equilibrium before applying P. Then we know the system must not rotate when P is applied at a given point. Hence we know the line of action of P because it must pass through the centre of mass.We can then work out the magnitude of P to give the desired vertical accelaration (the wording of the question has not excluded a horizontal component of accelaration, only rotation.)

    Hope that's helpful.
     
  6. Mar 24, 2010 #5

    berkeman

    User Avatar

    Staff: Mentor

    (two threads merged)

    Eddie123 and bazzz, are you the same person? Or just taking the same class?
     
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