Please help - Lever problem

  • Thread starter vedette
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  • #1
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I just started an intro to physics course this semester, and was given the following problem:

You are driving alone one evening and come upon a car accident. A victim is pinned beneath the car, which weights 1000 kg. You are not strong enough to lift the car by yourself and, in a panic, look around for some help. Nearby is a pile of boards and you decide to use a lever to lift the car. Describe how you would use the boards to lift the car. Assume that the longest board is 3 m long. In your answer, identify which class of lever you would use (which one has the highest M.A.?), what the E, R, EA, and RA would be, and what the mechanical advantage is. Use a drawing to illustrate how this lever would be set up.

I realize that this problem is probably ridiculously easy for some people, but I'm having a hard time figuring out how to set it up. I know I need to use a 2nd class lever, because they have the highest M.A. What I'm not sure of is what to use for a fulcrum (presumably another board) and where to set up the fulcrum. I'm not sure if it's possible with the information given, but I think you would have to put the 3 m board under the car, so that part of it extends out past the other side of the car (the resistance). If that's the case, would I just use different numbers for the RA until I came up with a result for Effort that seems like a logical amount of effort that I could exert by myself? I'm really confused, and any help would be appreciated! Thanks!
 

Answers and Replies

  • #2
3,042
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Try to use the longest board possible with the most distance from the end of the board to the fulcrum. You want the biggest lever arm. The max torque will be a force times a distance. You will always give it the max force you can, so the only way to up the torque is to increase the distance of the lever arm.
 
  • #3
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Thanks for your help with my lever problem - your answer helped me to see the problem more clearly.
 

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