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Rotations and Torque

  1. Mar 16, 2009 #1
    1. The problem statement, all variables and given/known data
    You need to open a heavy door that's 30 inches wide. Instictively, you push near the edge that's farthest from the hinges. If, instead, you had pushed at a point only 10 inches in from the hinges, how much harder would you have had to push to open the door at the same speed? Explain your answer.

    2. Relevant equations

    Here is my attempt at the problem below. I don't know where I'm making my mistake. Any help would be appreciated. Thanks.

    3. The attempt at a solution

    30 inches= .76 m
    Mass of Door-14 kg

    I=1/3 (14kg)(.25)2 Rotational Inertia
    1/3(14)(.063) I=1/3M/2
    1/3(.88) I=1/3 (14kg) (.58)
    .29 1/3 (8.12)
    2.7
    2.7/.29=9.3
     
  2. jcsd
  3. Mar 16, 2009 #2

    LowlyPion

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    Homework Helper

    Is it that hard?

    Isn't the same Torque required to open the door? Meaning same I and same a?

    So isn't the question what force acting at 1/3 the distance is needed to accomplish the same result?
     
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