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Using Vector in Determining Period of Pendulum Inside a Moving Train

  1. Mar 20, 2012 #1
    Hi all, i have a question relating to the period of pendulum. I got this question:
    A bob of mass 0.5 kg is suspended by a string from the ceiling inside a train moving on a straight level rail (to the right). If the train has an acceleration of 0.2g, what is the tension in the string when the bob is at rest with respect to the train? (picture 1)

    Someone explained to me that we must draw the tension as a vector joining the force by train to the pendulum and the pendulum's weight (picture 2). I don't understand. Isn't the pendulum supposed to be the resultant of those 2 forces (picture 3) and not the force by train who become the resultant (picture 2)?

    Please do explain. Thanks a lot.
     

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  2. jcsd
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