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    Here is the question! Please help, thank you.

    4)b) A uniform plank of weight 150N and of length 4m rests horizontally on two bricks. One of the bricks is at the end of the plank. The other brick is 1m from the other end of the plank.

    A child stands on the free end of the plank and just causes the other end to lift off its support. Calculate the weight of the child.
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    (Original post by Konnichiwa)
    Here is the question! Please help, thank you.

    4)b) A uniform plank of weight 150N and of length 4m rests horizontally on two bricks. One of the bricks is at the end of the plank. The other brick is 1m from the other end of the plank.

    A child stands on the free end of the plank and just causes the other end to lift off its support. Calculate the weight of the child.
    Have you attempted this yourself?
    What are you stuck on?
    I presume you have studied moments.
    Start by drawing a diagram, marking the forces and their positions along the plank. Can you do this?
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    Yes, I've completed that, I'll show you what I've done soon. One second, let me complete it again since I've seemed to have lost it.

    The answer to b) was 150N but I did not know how this was done.
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    Question a) was "Sketch the arrangement and calculate the support force on the plank from each brick.".

    I think this is correct.
    CALCULATING THIS WITHOUT THE CHILD...
    MOMENTS ABOUT Y:
    3X = 1*150;X=50


    MOMENTS ABOUT X:
    3Y = 150*2
    Y = 100.
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    Yes, the support forces are 100N and 50N
    Now for the second part...
    The key to doing this is a correct diagram.
    Without this you can't write down the moments and balance the clockwise with the anticlockwise.
    The clue is that there is no force from the support at the end when "A child stands on the free end of the plank and just causes the other end to lift off its support."
    This simplifies the problem.
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    Oops, I meant the answer was 150N.

    Is this the correct working out?
    Force Of Child = 1(150)?

    I really have no idea. I guess I may have to revise moments.
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    (Original post by Konnichiwa)
    Oops, I meant the answer was 150N.

    Is this the correct working out?
    Force Of Child = 1(150)?

    I really have no idea. I guess I may have to revise moments.
    Yes the child is 150N but it's not clear, without the diagram, how you got the answer.
 
 
 
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