1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Pendulum pin support reaction

  1. Aug 12, 2013 #1
    I've got a similar question to this for homework. I applied the same steps I used on my homework question to this problem and I get a different answer to the 299N that they have.

    Steps for my solution:
    1. Calculate the mass moment of inertia around the pin.
    2. Find the centre of mass of the pendulum.
    3. With the total mass of the pendulum going through the centre of gravity, I calculated the angular acceleration.
    [itex]\sum M = I_{0}\alpha[/itex]
    [itex]-M - l_{G}mg cos(45) = I_{0}\alpha[/itex]

    4. I calculated the normal and tangential accelerations.
    [itex]a_{n} = \omega^{2}l_{G}[/itex]
    [itex]a_{t} = \alpha l_{G}[/itex]

    5. I used D'Alembert's principle (F - ma = 0) for the tangential forces and Newton (F = ma) for the normal forces. Then I can find the magnitude of forces on pin. (The dotted line arrow in the diagram above is the inertial force for D'Alembert's principle.)

    I don't get the 299N stated as the answer in the original question but I can't see a problem with the steps I've gone through.
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Aug 12, 2013 #2
    Sorry, I made a mistake in reproducing the answer of 299N. The above method works.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted