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Homework Help: Speed Issue

  1. Sep 8, 2011 #1
    1. The problem statement, all variables and given/known data
    In coming to a stop a car leaves skid marks 92m long on the highway. Assuming a decceleration of 7.00 m/s^2 , estimate the SPEED of the car just before braking.

    I have a question though, is my approach ok? You can see my confusion in various parts of my procedures below, I guess it's the fact that it says find speed not velocity.

    2. Relevant equations
    Kinematic Equation for constant acceleration.



    3. The attempt at a solution

    Physics_2.png
     
  2. jcsd
  3. Sep 8, 2011 #2
    Speed=velocity lol
     
  4. Sep 8, 2011 #3
    I got -35m/s as my velocity though
     
  5. Sep 9, 2011 #4
    Speed is the magnitude of velocity and has no direction.

    EDIT: Assuming you are using the formula: v^2=u^2+2as you may need to check what you are using as v and u and be careful of your signs.

    0 = u^2 +2as
    u^2=-2as

    Does that make sense?
     
    Last edited: Sep 9, 2011
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