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Thread: Volumes and Mechanics questions

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    Volumes and Mechanics questions

    http://prntscr.com/ffbno6 - mechanics

    https://prnt.sc/ffa8xe - volumes

    Ty for any help!!
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    Re: Volumes and Mechanics questions

    Quote Originally Posted by pikachu975 View Post
    http://prntscr.com/ffbno6 - mechanics

    https://prnt.sc/ffa8xe - volumes

    Ty for any help!!

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    Re: Volumes and Mechanics questions

    Quote Originally Posted by pikachu975 View Post
    http://prntscr.com/ffbno6 - mechanics

    https://prnt.sc/ffa8xe - volumes

    Ty for any help!!

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    Re: Volumes and Mechanics questions

    Quote Originally Posted by InteGrand View Post
    I tried integrating so like

    a = -F/m
    and vdv/dx = -F/m
    dv/dx = -Fv/m
    dx = -mdv/Fv
    [x](0 to L) = -m/F [v^2 / 2](Vo to 0)
    L = m/F (Vo^2 / 2)
    F = mVo^2 / 2L

    But idk what I did wrong here
    2016 HSC (Accelerated)
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    Re: Volumes and Mechanics questions

    Quote Originally Posted by InteGrand View Post
    For the volumes I tried I keep getting 16 instead of 8 because I did:
    dV = 2pirh dy
    = 2pi * 2(1-y) * (2x)
    = 8pi (1-y)(2sqrt(1-y^2))
    = 16pi (1-y)(sqrt(1-y^2))

    Idk where I went wrong
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    Re: Volumes and Mechanics questions

    Quote Originally Posted by pikachu975 View Post
    For the volumes I tried I keep getting 16 instead of 8 because I did:
    dV = 2pirh dy
    = 2pi * 2(1-y) * (2x)
    = 8pi (1-y)(2sqrt(1-y^2))
    = 16pi (1-y)(sqrt(1-y^2))

    Idk where I went wrong
    It's not 2(1-y) but 1-y

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    Re: Volumes and Mechanics questions

    Quote Originally Posted by pikachu975 View Post
    For the volumes I tried I keep getting 16 instead of 8 because I did:
    dV = 2pirh dy
    = 2pi * 2(1-y) * (2x)
    = 8pi (1-y)(2sqrt(1-y^2))
    = 16pi (1-y)(sqrt(1-y^2))

    Idk where I went wrong

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    Re: Volumes and Mechanics questions

    Quote Originally Posted by pikachu975 View Post
    I tried integrating so like

    a = -F/m
    and vdv/dx = -F/m
    dv/dx = -Fv/m
    dx = -mdv/Fv
    [x](0 to L) = -m/F [v^2 / 2](Vo to 0)
    L = m/F (Vo^2 / 2)
    F = mVo^2 / 2L

    But idk what I did wrong here
    Basically the first line – it should be a = F/m. (Since F = ma.)

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    Re: Volumes and Mechanics questions

    Quote Originally Posted by InteGrand View Post
    Why is the radius only 1-y? Wouldn't it be 2(1-y) since 1-y only covers half the ellipse
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    Re: Volumes and Mechanics questions

    Quote Originally Posted by pikachu975 View Post
    Why is the radius only 1-y? Wouldn't it be 2(1-y) since 1-y only covers half the ellipse
    It doesn't cover half the ellipse. It's basically the shift of the curve. That's why it's (1-y) as the radius
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    Re: Volumes and Mechanics questions

    Quote Originally Posted by si2136 View Post
    It doesn't cover half the ellipse. It's basically the shift of the curve. That's why it's (1-y) as the radius
    Thanks heaps!
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    Re: Volumes and Mechanics questions

    Quote Originally Posted by InteGrand View Post
    If it wasn't a multiple choice, are you allowed to use physics formulae?
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    Re: Volumes and Mechanics questions

    Quote Originally Posted by frog1944 View Post
    If it wasn't a multiple choice, are you allowed to use physics formulae?
    Generally speaking, no.

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    Re: Volumes and Mechanics questions

    Ok, thanks
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    Re: Volumes and Mechanics questions

    Quote Originally Posted by frog1944 View Post
    Ok, thanks
    You'd use a = F/m and a = vdv/dx
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    Re: Volumes and Mechanics questions

    Quote Originally Posted by InteGrand View Post
    Basically the first line – it should be a = F/m. (Since F = ma.)
    why isn't it a=-F/m. The force is opposing the motion

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    Re: Volumes and Mechanics questions

    Quote Originally Posted by tsoliman1 View Post
    why isn't it a=-F/m. The force is opposing the motion
    We always have F = ma where F is the net force. The fact that the force is opposing the motion is reflected by the fact that F and a are negative.
    Last edited by InteGrand; 5 Jun 2017 at 4:13 PM.

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