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How do I figure out the initial velocity of an object?

  1. Jul 14, 2010 #1
    1. The problem statement, all variables and given/known data
    Hi, I need to figure out the initial velocity if an object of 1400 kilograms is subjected to a friction coefficient (sliding friction) of 0.4587 for 75.6 metres, and its final velocity after being subjected to that friction is 23.05 metres per second. How do I go about this?

    2. Relevant equations
    The only equations that I can think of that are relevant is:
    Fr=μmg
    distance=ut+0.5at2
    Ek=0.5mv

    3. The attempt at a solution
    Friction force= Fr=μmg
    Fr=0.4587*1400*9.8=6293.364
    Final momentum
    p=mv
    p=32270N
    Final Kinetic energy
    Ek=0.5mv
    Ek=0.5*1400*23.05=16135J
    I'm not sure how to do the distance equation as I don't know the amount of time.
     
  2. jcsd
  3. Jul 14, 2010 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Two ways to go:
    (1) Use kinematics. Use Newton's 2nd law to find the acceleration and combine that with some kinematic equations. (Look for a kinematic relationship that includes distance and velocity.)
    (2) Use energy. What's the work done by that friction force?

    FYI: KE = ½mv², not ½mv.
     
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