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Homework Help: Maximum acceleration of a front-wheel drive car

  1. May 6, 2013 #1
    1. The problem statement, all variables and given/known data
    In the badly loaded front-wheel-drive minibus shown in Figure Q26 the centre of gravity
    has been moved away from the driving wheels, determine the max acceleration possible in
    m/s2 if l=3.0 m, h=1 m, and the static co efficient of friction μs = 0.3.

    (Image is attached below)

    A - 2.12
    B - 0.89
    C - 1.34
    D - 1.63
    E - 1.15

    2. Relevant equations
    Ok well two possible equations, the one I used first of all was a = μs * g * fraction of g on front wheel (using moments)

    Although I have another equation which says a = μ * g * (distance from back wheel/(distance between wheels - μ * height))

    3. The attempt at a solution

    Using the first equation I get a = 0.3 * g * 1/3 = 0.98 ~ 0.89 Which is B
    Using the second equation I get a = 0.3 * g * (1/3-0.3) = 1.09 ~ 1.15 Which is E

    Are either of these equations correct? And if so which one?

    Edit Just realised that if I change the sign of the second equation to a + (1/3+0.3) I get exactly 0.89? Coincidence?

    Any help would be great

    Attached Files:

    Last edited: May 6, 2013
  2. jcsd
  3. May 6, 2013 #2


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    In your first attempt, the normal forces on the wheels do not split 2/3, 1/3 when the car is accelerating. In your second attempt, are you using some equation you found somewhere, or doing some calculation which you don't show?
  4. May 6, 2013 #3


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    No coincidence. Can you derive the correct form of the equation? Have you perhaps taken the equation you quoted from a different context?
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