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Homework Help: Not sure how to do this one

  1. Nov 6, 2008 #1
    1. The problem statement, all variables and given/known data

    A box with a mass of 5 kg sits in the middle of the bed of a pickup truck moving with a speed of 90 km/h. The maximum force of friction between the box and the truck is 15N. If the truck were braked uniformly to a stop in 125 m, would the box move? Justify your answer mathematically.

    2. Relevant equations

    vf2= vo2 + 2ax???

    3. The attempt at a solution

    a= (vf2 - vo2) / 2x
    a= (0-9) / 2(125)
    a= -0.36
    yes is would
    am i even close?
     
  2. jcsd
  3. Nov 6, 2008 #2

    mgb_phys

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    Almost correct .

    Calculate the acceleration of the truck - make sure you use consistent units.
    Then draw a diagram of the forces acting horizontally on the box, remember f=ma
     
  4. Nov 6, 2008 #3
    right so, 90 km/h is 25m/s. therefore acceleration [of truck] is equal to -0.1m/s2
     
  5. Nov 6, 2008 #4

    mgb_phys

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    Think you have a calculator error there
    a = v2/ 2s = 252 / 2*125 ms-2
     
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