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Published byAdelia Millicent Pope Modified over 9 years ago
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Conservation of momentum Collisions
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Homework answers 1a) 23,200 kg m/s eastward 1b) 38.4 km/h eastward, 10.7 m/s eastward 3a) 2.7 m/s same direction as original velocity 3b) 1.3 m/s in the same direction as original velocity 5a) 7,800 N opposite direction of motion 5b) 800 kg (too heavy to lift)
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Newton’s Cradle
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CONSERVATION OF MOMENTUM
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Pool and momentum
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What happens to the speed and/or direction of the cue ball after impact?
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Conservation of momentum If system is closed and isolated: Momentum in the system can not be created or destroyed, only transferred
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Conservation of momentum The total amount of momentum in a isolated system is conserved Conserved means that the momentum can be transferred from one object to another, but not lost to the system Isolated system: no other factors (forces) play a significant role in the interaction
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Closed environment No net gain or loss of momentum No additional outside forces
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Conservation of momentum In a closed isolated system, momentum won’t be created or destroyed, but can be transferred
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Is this roller coaster a closed system? Is it an isolated system?
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A pedal powered roller coaster “Sky Cycle” in Okayama, Japan
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Closed systems No truly closed, isolated systems But lots of systems that are significantly closed and isolated to allow use of the idea of conservation
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TYPES OF COLLISIONS
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Types Elastic: collision where KE and momentum are conserved, nothing sticks together Inelastic: collision where only momentum is conserved, nothing sticks together Completely Inelastic: collision where only momentum is conserved, objects stick together
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Example of Elastic Energy There are no examples of large scale perfectly elastic collisions Some of the kinetic energy of a moving object is converted into internal (ex. Thermal) energy of the other object involved in the collision, or converted to external TE (heating the surrounding environment)
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Most common type of collision is inelastic in nature
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EQUATION FOR CONSERVATION OF MOMENTUM Momentum of all object in system before interaction = Momentum of all objects afterward
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Equation for Conservation of Momentum Momentum of all objects in system before interaction = Momentum of all objects after the interaction p obj1 before + p obj2 before = p obj1after + p obj2 after
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Conservation of Momentum equation For 2 objects (can be expanded by adding a term on each side of equation for each additional object) m 1 v 1 + m 2 v 2 = m 1 v 1 ’ +m 2 v 2 ’
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Example problem #1 Two Car Collision… A 1500 kg car was paused at a stop sign, when a 3500 kg truck rammed into it from behind going 15 m/s. If the truck continues forward at 6 m/s after contact, what is the resulting velocity of the car? (assume no mass is lost or transferred in either vehicle during the interaction)
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Example Problem #2 A hockey player shots a 1.5 kg puck at 80 m/s that is caught by the opposing team’s 65 kg goalie. What is the resulting velocity of the goalie, who started from rest?
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HOCKEY (OCTOPUS ON ICE) Example of conservation of momentum
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Using conservation of momentum to solve for mass or velocity
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SHOOTING A GUN AND RECOIL Example of Conservation of momentum
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Shooting A Gun My experience with a sniper rifle What are the action reaction forces The amount of momentum in the gun and bullet before pulling the trigger and after
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Shooting a artillery piece or a pumpkin
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Using conservation of momentum to explain recoil
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Example #3 Mr. Baker shoot a 87g bullet from a 4.8 kg gun. The bullet leaves the gun at 600 m/s If both bullet and gun start from rest, what is the final velocity of the gun.
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Another example of conservation of momentum Recoil Rifle story
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Recoil Rifle story
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Math behind recoil Initial momentum of bullet and gun = 0 The sum of the momentums of both must total 0 Momentum of gun = -(Momentum of bullet)
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Stepping on a boat Jumping onto a moving hay ride Running into someone
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Momentum, reaction forces and shooting a gun
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Does the gun gain momentum when it fires a bullet?
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LAUNCHING A ROCKET Example of conservation of momentum
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What force makes the rocket move upward?
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How rockets move Fuel is ignited, particles move very fast. Particles push on the rocket Rocket pushes back sending particles down towards Earth The upward p of rocket = downward p of exhaust
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Conservation in 2 dimensions Grenade story Car accidents
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