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    Totally understood the theory and logic, but I think the questions in the book are purposely geared more towards the point that you need to select the correct variables for the problem:

    A particle of mass m moves in a straight line under the action of a resistive force of magnitude ke^(v/u) where u and k are constants. When t=0 the speed of the particle is u.

    Find the time during which the speed decreases to u/2.

    Pretty sure it's just been convoluted with variables on purpose. Although all the questions are like this. I've breezed through the rest of the chapter but I'm suddenly utterly stumped....!

    I know the answer is of the form t=f(u). I think the bit that's throwing me is the "when t=0, v=u" part. How/when/where I make use that fact?

    Sorry long post. Cheers all!

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    (Original post by stuart_aitken)
    Totally understood the theory and logic, but I think the questions in the book are purposely geared more towards the point that you need to select the correct variables for the problem:

    A particle of mass m moves in a straight line under the action of a resistive force of magnitude ke^(v/u) where u and k are constants. When t=0 the speed of the particle is u.

    Find the time during which the speed decreases to u/2.

    Pretty sure it's just been convoluted with variables on purpose. Although all the questions are like this. I've breezed through the rest of the chapter but I'm suddenly utterly stumped....!

    I know the answer is of the form t=f(u). I think the bit that's throwing me is the "when t=0, v=u" part. How/when/where I make use that fact?

    Sorry long post. Cheers all!

    Posted from TSR Mobile
    u is the velocity when t = 0 when solving a differential equation a constant needs to be found. This fact will enable you to express the equation in terms of u.
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    (Original post by joostan)
    u is the velocity when t = 0 when solving a differential equation a constant needs to be found. This fact will enable you to express the equation in terms of u.
    Aaaaaaaah I knew it! OK I didn't know, haha, but there was something 'extra' that I knew I'd totally overlooked. All makes sense now.

    Thanks bud :yy::yy::yy:

    I always hated the '+c' in integration because it seemed so needless at that general level. Finally its use is apparent!

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    (Original post by stuart_aitken)
    Aaaaaaaah I knew it! OK I didn't know, haha, but there was something 'extra' that I knew I'd totally overlooked. All makes sense now.

    Thanks bud :yy::yy::yy:

    I always hated the '+c' in integration because it seemed so needless at that general level. Finally its use is apparent!

    Posted from TSR Mobile
    No worries
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    (Original post by joostan)
    No worries
    OK I'm still lost.....

    Any idea for this one? (Image attached)...

    Best I can get is 4/(8t+1).....

    Name:  1365779815638.jpg
Views: 62
Size:  51.7 KB

    Cheers...! Major rep when I'm on my computer

    Sorry, it sounds like I'm just fishing for free answers now. I'm entirely self-taught so TSR is my only base for help...

    Edit... DONE IT!

    Cheers anyway though because I'm sure you'd have been able to help :yy:

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    (Original post by stuart_aitken)
    OK I'm still lost.....

    Any idea for this one? (Image attached)...

    Best I can get is 4/(8t+1).....

    Name:  1365779815638.jpg
Views: 62
Size:  51.7 KB

    Cheers...! Major rep when I'm on my computer

    Sorry, it sounds like I'm just fishing for free answers now. I'm entirely self-taught so TSR is my only base for help...

    Edit... DONE IT!

    Cheers anyway though because I'm sure you'd have been able to help :yy:

    Posted from TSR Mobile
    Sorry, I wasn't paying attention. Well Done. Thumb's up
 
 
 
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