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Displacement and Velocity Question

  1. Jun 11, 2014 #1
    Hi guys,

    Would really appreciate your thoughts on the question below.

    1. The problem statement, all variables and given/known data

    An object moves in a straight line and its displacement s at time t is given by -6t6-4t4+2. What is the velocity of the object at time t=7? Give the answer to the nearest whole number.

    3. The attempt at a solution

    I calculated the answer as being -610540. However, the question asks to give the answer to the nearest whole number and to me that seems absurd unless I have the wrong answer of course. Would really appreciate if someone could check my answer and let me know if it's correct or not.

    Thanks in advance. :smile:
  2. jcsd
  3. Jun 11, 2014 #2
    Usually on this site people are really finicky about not giving away answers, but this is a simple enough problem, and your answer looks good anyway.

    It's good to cross reference your answer with the question, but depend on that too much and you're going to stress yourself to death.
  4. Jun 11, 2014 #3


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    That answer looks good.
  5. Jun 11, 2014 #4
    Oh okay, I have no problem showing all my working as to how I arrived at the said answer. Like you said it's a simple problem but I don't understand why the question asks to give the answer to the nearest whole number?

    Surely it seems absurd to round such a large negative integer to zero? Is it just me or isn't that kind of odd? Unless of course I've managed to get the wrong answer. :smile:
  6. Jun 11, 2014 #5
    Thanks Sammy. :smile:

    I'm more confused on why the question wants me to give the answer to the nearest whole number. Surely it's kind of absurd to round such a high negative integer to zero?
  7. Jun 11, 2014 #6
    Don't worry about it too much. A lot of these questions are reworked from old examples, and have just had their exponents, conditions, and coefficients changed. Maybe at one point they used t=2.5? Either way, when you're confident in your answer, it's best to just move on.
  8. Jun 11, 2014 #7
    It's actually a computer quiz which counts towards my final grade. I only get 1 attempt at the answer so if the answer is incorrect I don't get the marks lol.
  9. Jun 12, 2014 #8


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    It is unsual in physics for data to be given without appropriate units. It would not surprise me to hear that the intended question involved somethng more than plain 7 nothing, and the rest of the text has somehow been lost, e.g. 7.1 seconds.

    Edit: Oh, it's a cmputer quiz. Likely they dropped the units in the interest of simplicity, then.

    Note: some computer quizzes use different data values for each candidate, to counter cheating by copying. So you got those coefficents, but others may have seen coefficients that included some fractions.
    Last edited: Jun 12, 2014
  10. Jun 12, 2014 #9
    It's part of a computer quiz so the units are usually left out. I think as you said the question is most likely a rewrite of a similar question but with a decimal value for t. I will just submit the negative integer value I obtained and hope for the best.
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