Initial velocity (and momentum)

  • Thread starter shiri
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  • #1
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A 2020kg car moving at 20.0m/s collides and locks together with a 1400kg car at rest at a stop sign. Show that momentum is conserved in a reference frame moving at 10.0m/s in the direction of the moving car.

initial momentum

final momentum


I don't understand why that the answer for initial momentum is not 20200 kg*m/s due to a reference frame moving at 10.0m/s in the direction of the moving car. Can anyone help me out here, that will be awesome
 
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  • #2
Doc Al
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In that new reference frame, what's the initial velocity (and momentum) of the 1400 kg car?
 
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  • #3
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In that new reference frame, what's the initial velocity (and momentum) of the 1400 kg car?

was it 10.0m/s and 14000kg*m/s in the opposite direction?
 
  • #4
Doc Al
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Exactly.
 
  • #5
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then do I have to sum it together (20200+ (-14000))kg*m/s? and the answer should be 6200kg*m/s for the initial momentum?
 
  • #6
Doc Al
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That's correct.
 
  • #7
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is that mean the final momentum is also 6200kg*m/s?
 
  • #8
Doc Al
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is that mean the final momentum is also 6200kg*m/s?
Sure. Momentum is conserved.
 
  • #9
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thanks Doc Al
 

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