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B Lifting one end of a canoe

  1. Jul 18, 2016 #1
    I read the responses in "Lifting one end of a beam" and presume my situation would be similar but not quite the same. A beam would have uniform mass throughout but a canoe probably doesn't.

    My question: If one end of a 70 pound (15 foot) canoe is sitting on the ground and I pick up the other end and set it on the canoe carrier on my truck, how much will I be lifting? Even though the canoe would probably not have a uniform mass throughout, the weight of one half of the canoe would equal the weight of the other half of the canoe, so my guess would be 35 pounds, probably slightly more since I would be lifting the canoe at a point a couple of feet in from the end.

    My reason for asking is I had heart surgery about 3 months ago and I'm supposed to be careful how much I lift. My wife told the cardiologist the canoe weighed 70 pounds, which is true, but I won't be lifting the entire canoe. I'm trying to determine a more precise weight so I can tell the cardiologist.
     
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  3. Jul 18, 2016 #2

    Simon Bridge

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    This is still a lever problem ... you are still lifting the entire mass of the canoe, it is just you are doing it through a lever where you have a mechanical advantage.
    If the mass of the canoe is symmetrically distributed then you can just use the distance tot he center of mass to help you. It is is not, then it will depend on which end you lift.
     
  4. Jul 18, 2016 #3

    CWatters

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    I doubt the cardiologist will tell you that any particular weight is ok/not ok. Best go back and ask him when he thinks it's safe to resume normal lifting. Meanwhile get your wife to help?
     
  5. Jul 18, 2016 #4

    Dale

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    I would suspect that it has more to do with heart rate and intrathoracic pressure. Get a Fitbit to monitor your heart rate, and make sure to not lift anything that requires you to grunt or hold your breath. Talk to your doctor and find out what is safe and stay well within those limits. Don't push it.

    Your estimate sounds good. Assuming a symmetrical canoe and a slow lift then it should be 35 lb. However, if the lift is fast or if you have to drag it then it could be substantially greater.
     
  6. Jul 18, 2016 #5
    If you lift one corner and the other corner stays on the ground, you should be lifting with about half the force. This is because the height of the center of mass is rising about 1/2 as much as the height of the corner you are lifting is. It's somewhat more complicated if the bottom is curved so the pivot moves when you tilt it, but I doubt you need an exact answer here. When calculating mechanical advantage, the product of distance and force should stay constant to achieve the same work.
     
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