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What is the spring constant of each spring

  1. Feb 17, 2009 #1
    1. The problem statement, all variables and given/known data

    A compact car has a mass of 1200 kg. Assume that the car has one spring on each wheel, that the spring are identical, and that the mass is equally distributed over the four springs. draw a picture of the situation.
    a) what is the spring constant of each spring if the empty car bounces up and down 2.0 times per second?
    b) what will be the cars oscillation frequency while carrying four 70 kg passengers.

    2. Relevant equations

    f = 1/2pie(k/m)^sq root

    3. The attempt at a solution

    m = 1200 kg
    f = 2 hz

    a) k = (2*pie*f)^2 * m = (2*3.14*2hz)^2*1200 kg = 189304.32 N/m

    b) m = (4*70)+1200 kg = 1480 kg

    f = (1/2*pie)(189304.32 Nm^-1/1480 kg) = 1.8 hz

    im not sure where I messed up.
     
  2. jcsd
  3. Feb 17, 2009 #2

    Doc Al

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    Staff: Mentor

    There are four springs, not one giant spring.
     
  4. Feb 17, 2009 #3
    so divide k by 4?
     
  5. Feb 17, 2009 #4

    Doc Al

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    Staff: Mentor

    Yes.
     
  6. Feb 17, 2009 #5
    so
    a) k = (189304.32 N/m)/4 = 47326.08 N/m

    and
    b) f = (1/2*pie)(47326.08 Nm^-1/1480 kg)^sq. root = 0.9 hz

    is it right?
     
  7. Feb 18, 2009 #6

    Doc Al

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    Staff: Mentor

    OK.

    No. What's the mass per spring?
     
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