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Can someone help me out in solving for delta t

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  1. Jul 3, 2015 #1

    Lmp

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

    Delta d = 0, v1 = 5.2 m/s, a = 9.8m/s^2 (down) delta t = ?
    2. Relevant equations

    d = v1 x t + 1/2 x a x t^2
    3. The attempt at a solution
    0 = (5.2 m/s) x t + 1/2 x (9.8 m/s^2) x t^2
    0 = t(5.2m/s - 4.9 m/s^2 x t^2)

    This is a sample question and states the answer is delta t = 0 or 1.1s. The problem is they don't show how they came with that answer. Could someone show how to get the final answer step by step....I emailed my online ilc support but never got an answer.
     
  2. jcsd
  3. Jul 3, 2015 #2

    berkeman

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    Staff: Mentor

    Welcome to the PF.

    Could you please provide the full problem statement? The problem statement as posted is pretty cryptic, and makes it hard to understand the context of the question. The problem looks to be pretty straightforward if the problem statement were made more clear. Thanks! :smile:
     
  4. Jul 3, 2015 #3
    And please add to the Relevant Equation section all equations of motion that you have in your arsenal of solving motion problems. Sometimes these are referred to the SUVAT equations, and it appears you have selected the incorrect equation to begin solving your problem.
     
  5. Jul 3, 2015 #4

    Lmp

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    I'll try my best....here I go...

    A ball is thrown upwards at 20.0m/s at an angle of 15 degrees from the ground find the final the total displacement.
    This is a sample question that goes through all the steps using trigonometric ratios to find the horizontal and vertical components.
    V1v = 5.2 m/s and v1h = 19.3 m/s
     
  6. Jul 3, 2015 #5

    berkeman

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    And the Relevant Equations that 256bits reminded you to post? Which ones do you think you should use on this problem?
     
  7. Jul 3, 2015 #6

    Lmp

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    I'm typing what is written in my on line course, this is a sample question where they show step by step on how to get the answer but when they come to how they solved for delta they don't show the final steps just what I posted already, they state the answer is 0 or 1.1s. I've tried to figure out how they got the answer but have no clue just wish someone could show me how they got the answer.....thanks in advance.
     
  8. Jul 3, 2015 #7

    SammyS

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    They used the zero product property of multiplication:

    If the product of two algebraic quantities is zero, then one of the quantities must be zero.

    It's pretty basic algebra.
     
  9. Jul 3, 2015 #8
    Well that is kind of weird that you have only one equation from your course.
    Look through your notes for some more equations from previuos days.
    SUVAT stands for Position (S) or displacement, Initilial veleocity (U) or Vo, final Velocity ( V) of Vf, accelearation (A), and Time (T).
     
  10. Jul 3, 2015 #9

    Lmp

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    I posted the relevant equation on my original post, I know this is the correct equation because that's what is written in my book for this example, I typed what's in my book under attempt to solve, but they go from what I've typed already to "and the answer is 0 and 1.1s" just want someone to show how they got that.
     
  11. Jul 3, 2015 #10

    Lmp

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    Thank anyway everyone, I guess I can't explain my situation properly.
     
  12. Jul 3, 2015 #11

    FactChecker

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    In your last equation, you forgot to reduce the exponent of t2 when you factored out t. So it should have been 0 = t * (5.2m/s - 4.9 m/s2 * t). One of the factors t and (5.2m/s - 4.9 m/s2 * t) must be 0. So either t = 0 or (5.2m/s - 4.9 m/s2 * t) = 0. The second option gives t=1.061 sec.
     
  13. Jul 3, 2015 #12

    Lmp

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    Thank you so much, I'm an ilc student "independent learning class" so I don't have anyone to ask and it's been a while since I've been in school. Again thank you very much.
     
  14. Jul 3, 2015 #13

    Lmp

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    Could you please show how you got t = 1.061 when you factor out for delta t, I just want to be 100% clear and you've been really helpful.
     
  15. Jul 3, 2015 #14

    FactChecker

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    If you have:
    5.2m/s - 4.9 m/s2 * t = 0,
    add 4.9 m/s2 * t to both sides of the equation to get
    5.2m/s = 4.9 m/s2 * t.
    Then divide both sides by 4.9 m/s2 to get
    1.06122 sec = t.
     
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