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Kinematics Mechanics

  1. Oct 8, 2016 #1

    Kajan thana

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    • Member advised to use the homework template for posts in the homework sections of PF.
    I have a question on kinematics, it is the second part of the question, there are two ways of doing the question the first way is straight forward ( one with ink writing ) but in the second method, the displacement is negative. Should it not be positive displacement? If it is negative displacement I will get into a complex number which we do not want.
    Someone, please help me.


    The question and my method will be attached to this post.
    Last edited by a moderator: Oct 8, 2016
  2. jcsd
  3. Oct 8, 2016 #2


    Staff: Mentor

    In future posts, please do not delete the homework template, which is required for homework questions.

    Also, we prefer that you include your work directly in this pane, not an image of your work. Although your work is fairly neat, the image is so small that it is hard to read (at least for me).

    You can write exponents by using the x2 icon in the menu bar at the top of this window. Other symbols are available by clicking the Σ icon in the menu bar. We also support LaTeX for more elaborate math expressions (see https://www.physicsforums.com/help/latexhelp/) under the INFO menu, in Help/How-To.
  4. Oct 8, 2016 #3

    Kajan thana

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    Yes but is it not easy to have a diagram which makes my working out clear?
  5. Oct 8, 2016 #4


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    Easy for whom? How can helpers point out or quote lines of your work if it's all in an image? And the work has no comments to say what each step is meant to accomplish. And I'm sure that your handwriting is clear enough to you, but others may find otherwise especially if their viewing devices are not optimal (say a small tablet or phone).

    Also, your "problem statement" image depicts two problems. You haven't identified which of the two you are working on.

    If you want to engage the help of volunteers, does it not make sense to make their job easier?
  6. Oct 8, 2016 #5

    Kajan thana

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    Yes I understand your point, but I have clearly mentioned that I am asking help for the second part of the question.
  7. Oct 8, 2016 #6


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    OK. So you are new to PF, so welcome. We will give you a small amount of latitude here, but what Mark says is absolutely true. Yes it may be easy for you to post an image of a diagram, and if it's easy to see clearly that's not so bad. But the people who help on this site are all volunteers - every one of us. Many of us have the attitude that if the student can't put in the effort to put the majority of their post in some editable text form, then maybe it's not worth our effort to type out a reply.

    As to the specifics of your thread:
    Your first image is helpful. It's clear and easy to read. It would have been more helpful had you indicated which problem you were solving.

    Regarding the image of the hand written solution, as Mark stated,
    and it's also hard for me to read.

    But since you're new here, I viewed the image in its own window allowing me to zoom in. When I do so and get it large enough to read comfortably, the image is so fuzzy that its readability is only slightly improved.

    Your first method:

    Your second method:

    First of all, if this is the method used to solve the same problem with the same given information, then use the same known data.

    The real problem with your execution of this method:
    The reason you get "complex solutions" is that the acceleration is in fact negative. You have it being positive.

    Attached Files:

  8. Oct 8, 2016 #7

    Kajan thana

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    Thank you, Sam, for your help. you have solved my problem. I will follow the procedure next time.

    Thanks again.
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