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Kinetic Energy and mass

  1. Nov 30, 2015 #1
    1. The problem statement, all variables and given/known data

    A) A car moving at 18 m/s is accelerated to 35 m/s. If the change in kinetic energy is 154 kJ, determine the mass of the car.

    2. Relevant equations

    KE = 0.5mv^2
    Kinetic energy = change in momentum = mv2-mv1

    3. The attempt at a solution

    Im not sure how to go about this problem, but I suspect that the mass can be obtained from the fact that kinetic energy is equal to the change in momentum?
  2. jcsd
  3. Nov 30, 2015 #2


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    Staff: Mentor

    Aren't these two equations contradictory? Which one is correct?
  4. Dec 1, 2015 #3
    KE=0.5mv^2 is the correct equation for kinetic energy, but we are given that.

    Am I right in saying that I need an equation that relates the change in Kinetic energy to mass?
  5. Dec 1, 2015 #4


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    Staff: Mentor

    Yes, and you already have all the ingredients to construct that equation yourself.
  6. Dec 1, 2015 #5

    If I were to say that Change in Kinetic Energy = mv2^2 - mv1^2

    Where v2 = final velocity and
    V1 = initial velocity

    Would I be on the right lines?
  7. Dec 1, 2015 #6


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    Science Advisor
    Homework Helper
    Gold Member

    Nearly, but you lost the 1/2.
  8. Dec 1, 2015 #7
    Perfect so,

    Change in Kinetic Energy = 0.5mv2^2 - 0.5mv1^2

    Thank you for your help DrClaude
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