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Levers (Moments)

  • Thread starter luysion
  • Start date
  • #1
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Homework Statement


A uniform 10 m long, 50 kg pole is lying on the ground. You get your little brother to lift at one end with an upward force of 100 N. How far from the other end will you need to lift so the pole stays horizontal (in m)? [Hint: Using your little brother as the fulcrum, what upward force, in N will you need to apply?]


Homework Equations





The Attempt at a Solution



Hi, Im really confused as to how to answer this. I know its to do with moments but i dont understand how to use the brother as the fulcrum because how much force does the other brother have to apply? the question doesnt say
 

Answers and Replies

  • #2
648
2
I think this is a poorly conceived question.
The other brother must lift with at least a force that will, when combined with the first brother, equal the weight of the the pole. In round figures (taking g as 10m/s²)
The weight is 500N and the one guy has an upward force of 100N, so you need at least 400N upwards. The question is, where do you apply that 400N to keep the pole horizontal; that is, there is no overall turning moment.
(At least that's what I think they mean!)
 

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