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Momentum Mo or r

Momentum Mo or r. What is Momentum?. A “quantity of motion" Tells that an object is on the move and hard to stop Mass in motion. Momentum Formula. Involves mass and velocity (so direction is important!) Momentum = Mass x Velocity Mo = MV ( r = MV) So… V = Mo/M and M = Mo/V

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Momentum Mo or r

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  1. MomentumMo or r

  2. What is Momentum? • A “quantity of motion" • Tells that an object is on the move and hard to stop • Mass in motion

  3. Momentum Formula • Involves mass and velocity (so direction is important!) • Momentum = Mass x Velocity Mo = MV (r = MV) • So… V = Mo/M and M = Mo/V The unit is a mass unit x a speed unit so… kg*m/s or kg*km/hr or g*cm/s… (it can’t be simplified more than this!)

  4. Lets Try a problem! These cars are about to collide… (on ice!) Mass: 300 kg Mass: 250 kg Velocity: 20 km/hr Velocity: 12 km/hr Mo = 300 kg x 20 km/hr Mo = 250 kg x 12 km/hr 6000 kg*km/hr3000 kg*km/hr Total Mo (Mo of 2 cars combined): 6000 + 3000 = 9000kg*km/hr

  5. The cars already collided. What is the total momentum after the crash? Mass: 300 kg Mass: 250 kg Velocity: 15 km/hr Velocity: 18 km/hr Mo = 300 kg x 15 km/hr Mo = 250 kg x 18 km/hr 4500kg*km/hr4500 kg*km/hr Total Mo: 4500 + 4500 = 9000 kg*km/hr

  6. So was momentum conserved? • YES!! • In a collision, the TOTAL MOMENTUM of all the objects combined is the same before and after the “crash” • Momentum is conserved if there is no loss of mass or energy due to friction… • Which never really happens (except when you are in a happy, theoretical world).

  7. Why did car 1’s speed decrease? • Remember action/reaction forces – if car 1 gives a force to car 2 (making car 2 speed up), then car 2 gives the same force back to car 1 - in the opposite direction – so car 1 slows down! • Car 1 transferred some Mo to Car 2 (1500 kg*m/s to be exact) • The car that loses Mo loses velocity… the car that gains Mo gains velocity

  8. What is the Total Mo here? Mass: 400 kg Mass: 300 kg Velocity: 35 km/hr Velocity: 40 km/hr Mo = 400 kg x 35 km/hr Mo = 300 kg x 40 km/hr 14000 kg*km/hr12000kg*km/hr Total Mo: 14000 - 12000 = 2000 kg*km/hr to the right The cars are going in opposite directions, so subtract the Mo!

  9. What is the total Mo after they collide? • Momentum is conserved! • So total Mo before = total Mo after • So the total Mo is still 2000 kg*km/hr (to the right)

  10. @%$&*!!! @%$&*!!!

  11. Before Collision Mass = 10, 000 kg Velocity = 5 m/s Mo = ? 10,000 kg x 5 m/s = 50, 000 kg x m/s

  12. Before Collision Mass = 5, 000 kg Velocity = 0 m/s Mo = ? 0 kg x m/s

  13. Total Momentum + 50,000 kg x m/s Momentum is Conserved – this is the total momentum before and after the crash!

  14. After Collision: Total Mo = 50,000 Mass = 5, 000 kg Mo = Mass = 10, 000 kg Velocity = 0 m/s Mo = ? 50,000 kg*m/s 0 kg*m/s The car gained 50,000 kg*m/s of Mo from the tank The tank lost 50,000 kg*m/s of Mo – this Mo was transferred to the car

  15. What happened to the speed of the car? Mass = 5, 000 kg Mo = 50,000 kg x m/s V = ? V = Mo / Mass = 50, 000 kg x m/s 5, 000 kg V = 10 m/s The speed of the car increased since it gained Mo! (remember the speed of the tank decreased)

  16. Oh noooooooo I am in sooo muuuch trouble!

  17. Mass = 5, 000 kg Mass = 6, 000 kg Velocity = 5 m/s Velocity = 0 m/s 5,000 kg x 5 m/s = 6,000 kg x 0 m/s = 25, 000 kg x m/s 0 kg x m/s Total Mo Before Collision = ? 25, 000 kg x m/s

  18. What happened to the Mo and speed of the cars after the collision? The car lost Mo… this Mo was transferred to the cop car So the car lost speed The cop car gained Mo from the patriotic car So the cop car gained speed The total Mo remained the same

  19. Combined Mass = 11, 000 kg (6,000 +5,000) Total Mo After Collision = 25, 000 kg x m/s (Mo is conserved!) Velocity of the wreck: 2.27 m/s – the cars have the same speed since they are moving together!

  20. Wait, how’d you do that? Since Mo = mass x velocity Velocity = Mo / mass 25,000 kg x m/s 11,000 kg 2.27 m/s

  21. What is the momentum of each individual car after the crash? Mass = 5,000 kg Velocity = 2.27 m/s Mo = 11,363.64 kg*ms The car slowed down and lost 13636.36 kg*m/s of Mo. Mass = 6,000 kg Velocity = 2.27 m/s Mo = 13,636.36 kg*ms The car sped up and gained 13636.36 kg*m.s of Mo The total Mo = 25,000 kg*m/s The amount of Mo the car lost = the amount of Mo the cop car gained!

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