Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Help Again Please

  1. Mar 16, 2005 #1
    This is the last question I will as for help on for this assignment I am doing I promise. For all you out there who know Physics you are awesome, cause boy is this stuff hard. Here is the question I am have trouble with now, again this could be an easy question but I am not sure on what to do. I have been trying to figure it out but no way can I do it.

    A student is trying to life a weight held in the hand. The distance from the elbow joint to the centre of gravity of the weight they are trying to life is 30cm. Their flexor muscles of the forearm insert 5cm from the centre of rotation of the elbow joint (the pivot). If the tendon inserts into the bone at an angle of 20 degrees, and the muscle is able to generate 40 kilograms of internal tension; How much weight could the student lift??

    I hate to be bothering for help but this assignment I am doing is worth 20% and I am hoping to do well, the rest of teh questions on this part I think I can handle. If someone could help me with this one it would be great.

    Thanks,Woody :confused:
  2. jcsd
  3. Mar 16, 2005 #2
    The student can lift (slowly) the weight while the torque (of the hand around the centre of rotation of the elbow joint) that is created by the tendon, which balances the torque created by the weight, is less then the value corresponding to the maximum force that the muscle can generate.

    To evaluate the maximum weight the hand we are talking about can lift we've got to write the equation of the torques around the elbow joint (it is the pivot) for the critical case:


    Solve it and get the answer;

    And take it easy! :wink:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook