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Calculating Speed with Kinematics

  1. Jan 24, 2007 #1
    I need help with this problem using the kinematic equations. My professor gave me the answer to this problem and wants to know the steps to achieve this answer.

    This is the example:
    The driver of a car slams on the brakes when he sees a tree blocking the road. The car slows uniformly with an acceleration of -5.60 m/s^2 for 4.20 s, making straight skid marks 62.4 m long ending at the tree. With what speed does the car then strike the tree?

    The professor's answer is:
    The speed is 3.10 m/s.

    Thank you in advance for taking the time to help me!

  2. jcsd
  3. Jan 25, 2007 #2
    Try using this equation:

    D = VoT + 1/2AT^2

    Where Vo is the initial velocity. Once you find this, it is fairly straightforward to calculate the final velocity. Or, for a simpler method, just enter it as a positive acceleration and Vo will work out to be the final velocity!
    Last edited: Jan 25, 2007
  4. Jan 25, 2007 #3
    Thank you for your help! I took your advice and it worked perfectly! I really appreciate the time and effort you took to help me!
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