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B How could a lever be used to lift the object

  1. Aug 1, 2016 #1
    Hello everyone!

    I'm new here and I have never been too good at physics, but now I've been trying to revise for the MCAT and I have stumbled across this question in "Kaplan MCAT Physics and Math Review":
    If you have and object three times as heavy as you can lift, how could a lever be used to lift the object? Where would the fulcrum need to be placed?

    I know the answer is obvious, and I have drawn the picture that I have attached to this post (where you place the fulcrum one quater of the way across the lever), but the textbook says that, alternatively, the fulcrum could be placed at the end with the object one-third of the way across the lever. It says that this would again result in a 3:1 ration of lever arms, meaning that only one-third of the original force is necessary, but I don't understand - how can there be a 3:1 when the object is placed one-third of the way across the lever?
    Could anybody please draw the alternative position of the fulcrum described in the textbook? I just can't picture it:(
     
  2. jcsd
  3. Aug 1, 2016 #2
    Sorry! I've just realised it's the wrong thread....
     
  4. Aug 1, 2016 #3

    A.T.

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  5. Aug 1, 2016 #4
    Thank you very much!
     
  6. Aug 1, 2016 #5

    sophiecentaur

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    Note the different directions of the forces for the three 'classes'. The choice could make a big difference to the choice in a practical situation. When the applied force would be downwards, it could be your weight and not your strength that would limit the maximum load. A weak, heavy person could find Class 1 very useful but an immensely strong lightweight would just manage to push himself up off the ground.
     
  7. Aug 1, 2016 #6
    I see, thank you!:smile:
     
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