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Conservation of Momentum

Conservation of Momentum. If a system of particles is isolated (no external forces acting on the system) the total momentum of the system is CONSERVED. Consider two particles that are isolated but interact with each other. They start with momenta p1 and p2.

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Conservation of Momentum

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  1. Conservation of Momentum If a system of particles is isolated (no external forces acting on the system) the total momentum of the system is CONSERVED. Consider two particles that are isolated but interact with each other. They start with momenta p1 and p2. Their action-reaction forces cause the momentum of each particle to change. m1 m2

  2. But is the total momentum, of the system! Over any time interval, the change in the total momentum is ZERO. As the individual particle momenta change, the TOTAL momentum of the system remains constant! Therefore,

  3. Conservation of Momentum: If there is NO NET EXTERNAL force acting on a system of particles, then the TOTAL MOMENTUM of the system remains constant. For a TWO particle system with masses m1, m2

  4. Isolated systems: • Ball falling towards Earth (ball and Earth) • Two objects colliding on a frictionless, horizontal surface • Fireworks (holds immediately before and after explosion) Momentum is conserved in all isolated systems EVEN IF KINETIC ENERGY IS NOT CONSERVED!

  5. Example 1: A 3000.0 kg cannon rests on a frictionless track. A 30.0 kg cannon ball is fired to the left horizontally. If the cannon recoils to the right with a velocity of 1.80 m/s, what is the final velocity of the ball? Ans: 1.80 x 10 2 m/s [Left] Example 2: A loaded railway car of mass 6000.0 kg is rolling to the right at 2.00 m/s when collides with an empty car (mass 3000.0 kg) rolling to the left at 3.00 m/s. The two car sticks together after the collision. What is the velocity of the pair after the collision? Ans: 0.330 m/s [right]

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