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Discussion in 'MCAT Study Question Q&A' started by amar21, May 30, 2008.

  1. amar21

    amar21 professional crammer 7+ Year Member

    Feb 27, 2006
    A 6 ft man lifts a 100-lb weight from the floor to a height 1 ft above his head.

    What force must be exerted by the man to sustain the object above his head?

    Answer: 100lb force

    NEVERMIND! i just figured it out... before I was figuring out why we didnt include the acceleration of gravity in calculating force

    F = mg, mg = W ...

    Fup = Fdown where Fnet =0 ... So... Fup=mg, Fup=W, Fup= 100
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  3. talkalot24

    talkalot24 Member 10+ Year Member

    Jul 21, 2004
    I still don't follow.

    W= mg = 100 * 10 = 1000 ???
  4. Soccerdoc11

    Soccerdoc11 2+ Year Member

    Apr 9, 2008
    Rochester, NY
    Lbs is a unit of Weight (Force) which already takes in account gravity
  5. Vihsadas

    Vihsadas No summer Moderator Emeritus Lifetime Donor Classifieds Approved 5+ Year Member

    Oct 17, 2007
    An Igloo
    That's right!
    For everyone else who might be reading, be careful to differentiate between lbs and Kg. We often take them interchangably in normal life because they differ only by some factor of gravity. But we have to remember that gravity has units associated with it, so the difference between lbs and Kg isn't just a numerical difference. It's a difference in the units too. One is a unit of mass (Kg) and one is a unit of force (lbs).
  6. pyromatic

    pyromatic Lord of Chaos 2+ Year Member

    Jul 17, 2006
    -------- SI <--------> English
    Mass: gram <-------> slug (no joke)
    Force: newton <-----> pound

    1 lb = (1 slug)*(1 ft/s^2) which is analogous to 1 N = (1 kg)*(1 m/s^2)

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