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Wheelbarrow and load advantage (i think)

  1. Mar 11, 2009 #1

    A wheelbarrow is holding a mass of 15kg, 35cm from the handle. The fulcrum is located 65cm from the handle. What is the mechanical advantage at the handle?

    Handle Load Fulcrum
    ____________ O (wheel)

    2. Relevant equations

    I believe it is (f1)x(d1)=(f2)x(d2)

    3. The attempt at a solution

    Therefore ...
    (f1)x(65)=(15)x(30) 30 being the distance from the handle to the centre of load.
    f1=450 / 65
    f1=6.9 kg

    Is this correct? I am a complete dummy at physics :(
  2. jcsd
  3. Mar 11, 2009 #2
    no, unfortunately you made a slight calculation error, but the rest is ok. your distance from the handle to the centre of the load is 35, not 30. Also, the term "mechanical advantage" gives me the feeling your answer should be in a ration or percentage form. ie. If I lifted the 15kg mass directly, it's mass is 15kg, if I use the wheelbarrow, it's apparent mass is 6.9kg. Therefore I have a mechanical advantage of 15/6.9=2.17 or (15-6.9)/6.9=117%

    Also, the wheel of your wheelbarrow is the fulcrum and it appears to be in a strange positon on your drawing. To approach this problem more accurately, you should draw a free body diagram, state that the system is equilibrium and let the sum of moments about your fulcrum be zero. You'll end up with the same result, but it will be neater and more rigid.

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