Principle of conservation of momentum question

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Discussion Overview

The discussion revolves around a problem involving the principle of conservation of momentum in the context of a space vehicle that separates into two sections. Participants explore how to apply the conservation of momentum to determine the velocity of the heavier section after separation and to calculate the change in total kinetic energy of the system.

Discussion Character

  • Homework-related
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant seeks help with a problem involving a space vehicle that separates into two sections of different masses and velocities.
  • Another participant questions the mass of the intact vehicle, suggesting it might be the sum of the two sections' masses.
  • Participants discuss the application of the conservation of momentum formula, with some expressing uncertainty about how to set up the equation with three masses involved.
  • There is a discussion about calculating the momentum of the intact vehicle and whether it equals the sum of the momenta of the separated sections.
  • One participant proposes a specific velocity for the heavier section after separation, while another confirms it seems correct.
  • There is a clarification about how to calculate the change in kinetic energy, with differing views on what should be subtracted to find this change.

Areas of Agreement / Disagreement

Participants generally agree on the application of conservation of momentum, but there is uncertainty regarding the specific calculations and the interpretation of kinetic energy changes. No consensus is reached on the exact values or methods for calculating kinetic energy.

Contextual Notes

Some participants express uncertainty about the initial mass of the vehicle and how to incorporate it into the momentum conservation equation. There are also unresolved questions about the calculations for kinetic energy changes.

dansbr
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1. Somebody help explain how to do this for me, am not looking answer, an explanation so i can solve it would be great.

A space vehicle traveling at a velocity of 7000km/h separates into two sections of mass 1100kg and 200kg. the two parts continue moving in the same direction with the lighter section moving at 10000km/h.

Determine the velocity of the heavier section after separation
The change in the total kinetic energy of the system



2. I know to use the conservation of momentum (M1U1 + M2U1 = M1V1 + M2V2), but since there are three values for mass am not sure where to begin.



3. any attempt i have made has been unsuccessful

Cheers :)
 
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What's the mass and velocity of the space vehicle before it breaks up?
 
the space vehicle is traveling at 7000km/h. i don't know the mass of it but wouldn't it be the sum of the sections so 1100+200=1300kg
 
dansbr said:
the space vehicle is traveling at 7000km/h. i don't know the mass of it but wouldn't it be the sum of the sections so 1100+200=1300kg
Exactly. So now you have one side of the momentum conservation equation. Set the initial momentum (of the intact vehicle) equal to the sum of the momenta of the sections after it breaks up.
 
So if momentum is f=mv
Would the momentum of the intact vehicle be (200x10000)+(1100x v?)
Am still not sure about this
 
dansbr said:
So if momentum is f=mv
Would the momentum of the intact vehicle be (200x10000)+(1100x v?)
Am still not sure about this
The momentum of the intact vehicle is its mass (which you figured out already) times its velocity (which is given).
 
So the momentum of the intact vehicle is 1300x7000=9100000
Does that mean the sum of the momentums of the separate parts equal the momentum of the intact vehicle.
 
That's what conservation of momentum is about.
 
dansbr said:
So the momentum of the intact vehicle is 1300x7000=9100000
Does that mean the sum of the momentums of the separate parts equal the momentum of the intact vehicle.
Exactly. When something is "conserved" that means it stays the same. The total momentum of the of the vehicle (or its parts) doesn't change when it breaks up.
 
  • #10
Is the answer 6454km/h
 
  • #11
dansbr said:
Is the answer 6454km/h
Looks right.
 
  • #12
Then would the change in kinetic energy of the system be the kinetic energy of the intact vehicle minus the kinetic energy of the heavier of the two separate bits?
 
  • #13
dansbr said:
Then would the change in kinetic energy of the system be the kinetic energy of the intact vehicle minus the kinetic energy of the heavier of the two separate bits?
Not exactly. The change in KE is the total KE after the break up (both pieces) minus the initial KE (of the intact vehicle).
 
  • #14
Thanks good help
 

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