Results 1 to 9 of 9

Math Help - SUVAT - Motion Equation

  1. #1
    Member
    Joined
    Sep 2009
    Posts
    79

    SUVAT - Motion Equation

    This has something to do with graphing (speed time graph) so I suspect this is the right forum.

    Question: Two stations A and B are 495m apart. A train starts from A and accelerates uniformly for 15s to a speed of 54kmh^{-1} which it maintains until it is 90m from B. Sketch a speed-time graph to show the motion of the train. Find the magnitude of the acceleration and retardation and the total time the journey takes.

    I'm stuck on the magnitude of acceleration =\ .
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor
    Joined
    Sep 2008
    From
    West Malaysia
    Posts
    1,261
    Quote Originally Posted by Viral View Post
    This has something to do with graphing (speed time graph) so I suspect this is the right forum.

    Question: Two stations A and B are 495m apart. A train starts from A and accelerates uniformly for 15s to a speed of 54kmh^{-1} which it maintains until it is 90m from B. Sketch a speed-time graph to show the motion of the train. Find the magnitude of the acceleration and retardation and the total time the journey takes.

    I'm stuck on the magnitude of acceleration =\ .

    HI

    Have you tried s=ut+\frac{1}{2}at^2 ?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Member
    Joined
    Sep 2009
    Posts
    79
    I'm not sure what it means by magnitude of acceleration. Because when we've seen magnitude before, we used pythagoras to get the hypotenuse of the triangle for the magnitude >< .
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor
    Joined
    Sep 2008
    From
    West Malaysia
    Posts
    1,261
    Quote Originally Posted by Viral View Post
    I'm not sure what it means by magnitude of acceleration. Because when we've seen magnitude before, we used pythagoras to get the hypotenuse of the triangle for the magnitude >< .
    It means value , in this case value of the acceleration , just that this value is never negative . So use the formula i gave you to find its magnitude .
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Member
    Joined
    Sep 2009
    Posts
    79
    Ahh, so it's always the absolute value of the acceleration?

    EDIT: So I find the magnitude of the acceleration, then the magnitude of the retardation and find the difference?
    Follow Math Help Forum on Facebook and Google+

  6. #6
    MHF Contributor
    Joined
    Sep 2008
    From
    West Malaysia
    Posts
    1,261
    Quote Originally Posted by Viral View Post
    Ahh, so it's always the absolute value of the acceleration?

    EDIT: So I find the magnitude of the acceleration, then the magnitude of the retardation and find the difference?
    yes .

    Not quite true . THe train accelerates until a point 90 m before B . Then from here , the train decelerates until station B .

    So for acceleration , you know s=405 m , u=54 km/h (convert this to m/s) , and t=15 s

    so by s=ut+1/2at^2 , you can find a .

    Now for deceleration ,

    s=90 , u=54 km/h (again , do the conversion) , v=0

    use v^2=u^2+2as , you should get a negative value for a since its deceleration.
    Follow Math Help Forum on Facebook and Google+

  7. #7
    Member
    Joined
    Sep 2009
    Posts
    79
    I realised that I did not have the displacement from the first motion of acceleration. Therefore I used v=u+at and worked out the right answer of 1ms^{-1}. I successfully worked out the retardation as 1.25ms^{-1}.
    Follow Math Help Forum on Facebook and Google+

  8. #8
    MHF Contributor
    Joined
    Sep 2008
    From
    West Malaysia
    Posts
    1,261
    Quote Originally Posted by Viral View Post
    I realised that I did not have the displacement from the first motion of acceleration. Therefore I used v=u+at and worked out the right answer of 1ms^{-1}. I successfully worked out the retardation as 1.25ms^{-1}.
    Are you sure those are the answers given ? by the way , your unit is wrong too .
    Follow Math Help Forum on Facebook and Google+

  9. #9
    Member
    Joined
    Sep 2009
    Posts
    79
    yep they're the right answers (and those were typos, they should be ms^{-2}.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Another SUVAT Question
    Posted in the Math Topics Forum
    Replies: 1
    Last Post: February 4th 2010, 11:46 PM
  2. SUVAT Question
    Posted in the Math Topics Forum
    Replies: 1
    Last Post: February 4th 2010, 02:12 PM
  3. SUVAT(time)
    Posted in the Math Topics Forum
    Replies: 3
    Last Post: February 4th 2010, 09:06 AM
  4. SUVAT help please (mechanics)
    Posted in the Math Topics Forum
    Replies: 1
    Last Post: January 19th 2010, 01:46 PM
  5. SUVAT equation help!!
    Posted in the Calculus Forum
    Replies: 1
    Last Post: September 24th 2007, 09:45 PM

Search Tags


/mathhelpforum @mathhelpforum