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Is this assumption correct? (dynamic friction)

  1. Jun 3, 2009 #1
    A particle of mass M slides on a horizontal surface with coefficient of (dynamic) friction
    μ = 0.4. At time t = 0 it is 1m from a vertical wall, moving at 6 m/s perpendicularly towards it. When does it strike the wall? ( You may assume it is less than 1 second)

    2. Relevant equations

    friction = μ x N

    where N is the normal force

    suvat equations

    3. The attempt at a solution

    friction = μ x N

    M x a = μ x M x g where g = 10 m/s^2

    a = 0.4 x g = 4 m/s^2

    I want to know if I can take this as a deceleration? Therefore hitting the wall with a velocity of :

    v^2 = u^2 + 2as where u = 6 m/s s = 1m a = -4 m/s^2

    v = 5.29 m/s

    and where the time taken is :

    v = u + at

    t = 0.1775 seconds
  2. jcsd
  3. Jun 3, 2009 #2


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    Staff Emeritus
    Science Advisor
    Gold Member

    I've not checked your arithmetic, but your method looks fine to me.

    One minor point: you have used two SUVAT equations here. However, if you would have used the equation s = ut + 1/2at2, you could have cut your working in half.
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