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Friction/acceleration question

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    The driver of a car travelling in a straight line, level road suddenly brakes.
    The car slides 10m in 2 seconds before stopping. Assuming constant deceleration, find the co-efficient of friction between the tyres and the road.

    I got given this question as homework after doing a lecture on turning moments so that put me on the wrong foot straight away.

    So ive assumed I need to find the velocity first using d/t the find the acceleration using s=u.t + 0.5.a.t2

    but then im lost. Can anyone point where im going wrong?
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    You need to use F_f=\mu F_n

    The normal reaction F_n = mg, and the frictional force F_f=ma

    So you just need to calculate the acceleration of the car, and then you can find \mu
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    so do I need the mass value to complete this?
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    No, the mass cancels out
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    would you also use this method for this question

    Click image for larger version. 

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    or would this be better solved using the energy method?

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Updated: May 20, 2012
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