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Conservation of energy or conservation of momentum

  • Thread starter salami
  • Start date
  • #1
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OK this is about a bullet hitting a block on wheels (inelastic collision), no friction or energy losses in the problem.

I'm trying to find Velocity of the system after collision

Why is it that if I use conservation of momentum I get a different answer of V than if I used conservation of Kinetic energy.

Momentum
m1*v1=(m1+m2)*v2

K energy
0.5*m1*v1^2=0.5*(m1+m2)*v2^2

You can make up your own numbers....I just dont understand the physics!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 

Answers and Replies

  • #2
Doc Al
Mentor
44,874
1,122
It's an inelastic collision--energy is not conserved. Mechanical energy will be lost.
 
  • #3
G01
Homework Helper
Gold Member
2,665
16
The reason you get different numbers is that mechanical energy is NOT conserved in an inelastic collision, while momentum is.
 

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