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I Some calculations in Newton's Third Law

  1. Jul 1, 2017 #1
    1- IF we have an object has 200 kg and we also have a machine has 5 kg and pushes that object with force of 600 n , in newton third law it must be another force =-600n then : the acceleration of the object must be 3 m\s^2 and the acceleration of the machine is 120 m\s^2 , Am I wrong??

    2- if I am in vacuum and I dropped an apple and the distance between my hand and the floor =5 m , is the apple must lunge with 5 m also?? (I said vacuum because I think that the thing causes apple not lunge at the same distance is the air resistance )

    And thank you.
  2. jcsd
  3. Jul 1, 2017 #2


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    You are essentially correct, but be careful about the signs of the accelerations. They would be in opposite directions, so they would have opposite signs in any coordinate system.
    I don't understand your use of the word "lunge" here.
  4. Jul 1, 2017 #3
    sorry I am not talk English extremely ,I am from egypt
    I meant Rebound
    and thank you
  5. Jul 1, 2017 #4


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    Ok. The rebound height would depend on the elasticity of the object. Something with perfect elasticity would bounce back to 5 m (ignoring the reaction motion of the Earth). A real apple would primarily squash instead of bouncing. The coefficient of restitution tells how much the object will bounce. (see https://en.wikipedia.org/wiki/Coefficient_of_restitution )
  6. Jul 2, 2017 #5
    If there's no loss of energy due to rebounding or anything else, then yes, you are correct on both.
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