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Homework Help: Newtons 2nd Law Problems

  1. Oct 7, 2006 #1
    I really need help with this question. Ive tried solving it but i just cant do it.

    The question

    A loaded dump-truck having a total mass of 2.4*10power of 4 kg is travelling east at 85km/h.The truck driver can apply a braking force of 5.5*10 power of 4 to the wheels without causing the wheels to lock and skid. Calulate:
    A)the maxium negative acceleration of this trunk.(in m/s2)
    B)the minimum stopping time
    C)the minimum stopping distance

    The only thing I know is the mass. I know you are supposed to use the 85km/h for something I can not figure out for what.
  2. jcsd
  3. Oct 7, 2006 #2

    Chi Meson

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    A) Newtons 2nd Law. What is it? As the truck brakes, what is the only unbalanced force on it?
  4. Oct 7, 2006 #3


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    Well, one has a mass 24000 kg, and a braking force of 55000 N (I guess N) based on the problem.

    a) Apply F = ma, or a = F/m.

    b) From a and the initial velocity, 85km/h (convert to m/s) compute the time that it takes for the truck to decelerate to v = 0 m/s.

    c) From a and the initial velocity, compute the distance for the truck to decelerate to v = 0 m/s.


  5. Oct 7, 2006 #4
    what is 85km/h

    what does 85km/h stand for and what do I use it for
  6. Oct 8, 2006 #5


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    85 kilometers per hour, I'd venture.

    - Warren
  7. Oct 8, 2006 #6
    That's your initial velocity and you have to do something with the units. Refer to the link Astronuc put up for the constant acceleration equations.
  8. Oct 9, 2006 #7

    Thanks so much for the help i tried your methods and they seem to work.
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