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Need help with Kinematics

  1. May 30, 2006 #1
    Are there any hints in problems that can help me pick out which of the 4 equations are to be used ? :confused: :confused:
  2. jcsd
  3. May 30, 2006 #2
    What four equations are you refering to? A good hint is to, before you start trying to do a problem, write down every variable that you know the value of, and then write down the variables you are supposed to solve for, look for equations that lead you from your knowns to your unknowns. This is a good short term solution.

    In the long term, try, before doing every problem, to think through what the different equations mean, physically, not mathematically, in the long run you will gain an intuition about what you are solving for and what should be in equations, making the job of remembering equations and thinking through problems much easier.

  4. May 30, 2006 #3
    My head hurts :rolleyes:

    Just not an easy subject for me to catch onto. I will post the equations but thanks for the hints.
  5. Jun 2, 2006 #4
    i was gonna make a thread on this as well

    we are given 4 kinematics eq, for example in the x-axis

    1) V (final) = V (initial) + at

    2) X = 1/2 (V initial + V final)t

    3) X = V (initial)t + 1/2 at(squared)

    4) V (final squared) = V (inital squared) + 2ax

    typically solving kinematics problems involving writing down wat is given which i always do and the general layout of a kinematics in 2d question is usually like "guy kicks a ball at 28 degrees above the horizontal at a speed of 16m/s towards a goal post 16.8m away, solve for final velocity".

    i did the qn twice using eq 1 and 4 to solve for final velocity, both times it gives a diff ans and only one was the correct one

    from my understanding it appears to be no differences between eq 1 and 4 but when solving the problem, both eq leads to very different answers. in this case how do i know which is the correct equation to apply?
    Last edited: Jun 2, 2006
  6. Jun 2, 2006 #5


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    You have a obviously made an error in one of your steps, both equations are valid provided you apply them correctly. However, equation 4 seems the obvious choice here as you are given all the required variable, whereas in equation one you have to calculate time.

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