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KE1 vs KE2, mechanical energy change

  1. Mar 23, 2016 #1
    1. The problem statement, all variables and given/known data
    If two objects of unequal mass and unequal Kinetic energy hit each other, they lose some energy to other forms but keep enough to do Work on each other. A good example is a car and wind, a man and ball could also apply, a ball with KE could stop a running man if KE does work, though that is hard to do as energy is taken up many other forms- - back to car and wind, wind moving has mechanical energy in the form of Kinetic energy and a car has Kinetic energy, If a Car with 700 Joules of KE is moving to the right and a gust of wind with 1400 Joules from the left, what happens to the car and the wind?

    2. Relevant equations

    3. The attempt at a solution
    The wind has Mechanical energy in the form of Kinetic energy, this allows the wind to apply a force, doing work by a non-conservative force as a air particles convert KE which is ME into non-conservative work, transferring energy to what it hits. The wind will be able to apply a non-conservative force, thus altering the mechanical energy of what it hits. A car with 700Joules, so TMEi-Car + (-TMEi-Wind)= TMEf

    (700Joules)+(-1400Joules)=700Joules TMEf, the Car is stopped and then moved backed, the wind is doing work, the wind stopped the car and had 700 Joules left to push the car backwards.

    What is wind and its KE used for? Wind farms! wind with KE does work onto the blades of wind mills, the applied non-conservative force pushes the blades giving them KE which is ME, thus that ME is turned into power, electrical energy - - however, power is created which is supplied to homes and schools, thus Mechanical energy in both forms PE and KE is able to do work.
  2. jcsd
  3. Mar 23, 2016 #2


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    I think this is quite a badly designed problem. The problem statement says..

    Sure but unless you know how much energy is lost "to other forms" you have no way to determine if the car slows a little or stops and gets blown backwards.
  4. Mar 23, 2016 #3

    yep, Typo's hahahaha My bad

    however, the equation is and numbers are set.
  5. Mar 23, 2016 #4


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  6. Mar 23, 2016 #5
    Well, okay just assume some energy is lost, and the remaining energy is 700Joules and 1400Joules to do work...
  7. Mar 24, 2016 #6


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    If the wind gust contains 1400 Joules and 700 are lost then only 700 are available to do work on the car.
  8. Mar 24, 2016 #7
    Well, the 1400joules lost 700joules to stop the 700joule car and the remaining 700joules pushes the car back, that is the question.

    It would can be said that Two objects opposite of each other with KE can do non-conservative work on each other.

    The wind has finite KE and so does the car, if the energy goes to applying a non-conservative force and thus a non-conservative force the wind has superior KE, so it stops the car and then pushes it back.

    Also, the car would be stopped in a short distance then pushed back
  9. Mar 25, 2016 #8
    My previous answer is correct, it would be best to say that KE can do work even with two colliding objects as long as energy remains to do non-conservative work on the whole body, correct?
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