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Math Help - Mass spring problem

  1. #1
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    Mass spring problem

    I'm confussed to the workout of this problem.

    Given a mass of 2kg, stretches a spring .392m (m i believe here is meters). At all times the damping device gives a resisting force whose magnitude in Newtons is twenty times the magnitude of the velocity in m/s. The mass is released from the equilibrium position with an upwards velocity of 5m/s. How far from the equilibrium position does the object get.
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  2. #2
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    Re: Mass spring problem

    Okay, what have you done on this? Can you write the equation for this motion?
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  3. #3
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    Re: Mass spring problem

    I'm using the equation my''+by'+ky=0. Where i'm confused is the statment of 20 times the magnitude of the velocity, which is a rate. Where do i use that rate in the equation? Where m=mass b=damping coefficient k=spring constant
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  4. #4
    Senior Member MaxJasper's Avatar
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    Lightbulb Re: Mass spring problem

    Try to find a solution like:

    y(\text{t})\text{=}e^{\frac{\left(-b-\sqrt{b^2-4 g k m}\right) t}{2 g m}} \text{C1}+e^{\frac{\left(-b+\sqrt{b^2-4 g k m}\right) t}{2 g m}} \text{C2}

    then find c1 & c2 based on y(0)=5....etc.
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  5. #5
    MHF Contributor ebaines's Avatar
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    Re: Mass spring problem

    Quote Originally Posted by nivek0078 View Post
    I'm using the equation my''+by'+ky=0. Where i'm confused is the statment of 20 times the magnitude of the velocity, which is a rate. Where do i use that rate in the equation? Where m=mass b=damping coefficient k=spring constant
    They tell you that the damping force is "twenty times the magnitude of the velocity in m/s," which means that the value of 'b' is -20 N/(m/s). Also note that the signs of both the 'b' and the 'k' coefficients is negative (force of the spring is in a direction opposite to its displacement, and force of the damper is in a direction opposite its velocity).
    Last edited by ebaines; October 10th 2012 at 12:47 PM.
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  6. #6
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    Re: Mass spring problem

    Can you write the equation for this motion?

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  7. #7
    MHF Contributor ebaines's Avatar
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    Re: Mass spring problem

    Quote Originally Posted by addictionshary View Post
    Can you write the equation for this motion?
    To whom are you directing this question? Note that the OP posted his question over 6 months ago, so I'm sure he has completed his homework assignment long ago.
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