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    I feel like it's easy but I just can't do it for some reason. What am I missing?

    I've tried:

    If s = 15, but you can't sub t in so how do you find out A?
    If s = 0, t = 0, and you can't find A here.
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    (Original post by 2014_GCSE)
    Name:  ScreenShot016.jpg
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    I feel like it's easy but I just can't do it for some reason. What am I missing?

    I've tried:

    If s = 15, but you can't sub t in so how do you find out A?
    If s = 0, t = 0, and you can't find A here.
    What else do you know when t=0?
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    (Original post by morgan8002)
    What else do you know when t=0?
    initial velocity = 20

    Do I differentiate the equation and put it equal to 20?
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    (Original post by 2014_GCSE)
    initial velocity = 20

    Do I differentiate the equation and put it equal to 20?
    yeah
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    (Original post by morgan8002)
    yeah
    Thanks for helping me here but urhh I'm still having trouble haha

    so

    S = A - Ae^-kt
    V = kAe^kt

    20 = kAe^k(0)

    20 = kA

    What have I done wrong...?
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    (Original post by 2014_GCSE)
    Thanks for helping me here but urhh I'm still having trouble haha

    so

    S = A - Ae^-kt
    V = kAe^kt

    20 = kAe^k(0)

    20 = kA

    What have I done wrong...?
    Sorry. I looked at the question quickly and didn't take into account the extra k when differentiating.
    Sketch a graph of s against t. What happens as t \rightarrow \infty? This is another common way of getting around the problem and removing the ks.
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    (Original post by morgan8002)
    Sorry. I looked at the question quickly and didn't take into account the extra k when differentiating.
    Sketch a graph of s against t. What happens as t \rightarrow \infty? This is another common way of getting around the problem and removing the ks.
    S gets bigger and moves towards the asymptote of A?
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    (Original post by 2014_GCSE)
    S gets bigger and moves towards the asymptote of A?
    Yes. The question says that the particle stops at s=15m, so this is the value of A.
 
 
 
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