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Math Help - Distance - velocity - acceleration

  1. #1
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    Distance - velocity - acceleration

    Hi! I need help with this problem, it's really confusing me...

    The displacement s metres from point O of a particle travelling along a straight line through O, after t seconds, is given by

    s= 2..8t^3-t^4 , 1<t<3
    Question: Calculate the value of t when the particle reaches O.

    Thanks!
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  2. #2
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    Hello !
    Quote Originally Posted by thegirlwhoneedshelp View Post
    Hi! I need help with this problem, it's really confusing me...

    The displacement s metres from point O of a particle travelling along a straight line through O, after t seconds, is given by

    s= 2..8t^3-t^4 , 1<t<3
    Question: Calculate the value of t when the particle reaches O.

    Thanks!
    If I understood correctly your question, that's what you have to do :

    Find t such that s=0, because when the particle reaches point O, the displacement from point O will be 0 !
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  3. #3
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    Quote Originally Posted by Moo View Post
    Hello !

    If I understood correctly your question, that's what you have to do :

    Find t such that s=0, because when the particle reaches point O, the displacement from point O will be 0 !
    So I have to write 2.8t^3-t^4=0 and isolate t, how do I do that?
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  4. #4
    Moo
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    Quote Originally Posted by thegirlwhoneedshelp View Post
    So I have to write 2.8t^3-t^4=0 and isolate t, how do I do that?
    Factorise by t^3 :

    2.8t^3-t^4=t^3 \cdot (2.8-t)

    Note that a product of numbers is equal to zero if and only if at least one of its factor is equal to 0.

    So either t^3=0, either 2.8-t=0

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    Oh! and how do I find the displacement, in m, whenthe particle comes to rest in the same problem?
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  6. #6
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    Quote Originally Posted by thegirlwhoneedshelp View Post
    Oh! and how do I find the displacement, in m, whenthe particle comes to rest in the same problem?
    Hmmm Okay, I'm lost on it, I don't understand what you've said

    Is it possible for you to restate that or to say it in French ?
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  7. #7
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    Lol! I mean that I have to find the distance between the point O and the particle when the velocity is 0... I would know how to find the time but not this...
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  8. #8
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    Quote Originally Posted by thegirlwhoneedshelp View Post
    Lol! I mean that I have to find the distance between the point O and the particle when the velocity is 0... I would know how to find the time but not this...
    Ok, so it looks like you're able to find the velocity (by differentiating).
    Solve for t in velocity=0.
    You'll get a certain time. Substitute it in the displacement formula to get the distance ! It's just logic, so think a little
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  9. #9
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    Oh yeah! I forgot I could do that! lol! Im just tired^^
    Thanks!
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