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Linear Momentum
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5-1 Linear Momentum
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Linear Momentum, p – defined as mass x velocity The unit is kgm/s A quantity used in collisions So a small object with a large velocity could have the same momentum as a large object with a small velocity 9-1 Linear Momentum
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5.2 Momentum and Newton’s Second Law
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Newton’s Second Law is This is only true for objects with a constant mass The original form of the equation was This statement is true even if the mass varies 5.2 Momentum and Newton’s Second Law
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5.3 Impulse
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A baseball player hits a pitch Bat delivers an impulse We actually on consider average force Impulse is define as 5.3 Impulse Impulse Sim
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An increase in time produces a decreases in force A decrease in time produces an increase in force 5.3 Impulse Airbag
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5.4 Conservation of Linear Momentum
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If no net external force is applied to a system Then momentum is conserved 5.4 Conservation of Linear Momentum Explode Sim
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External Forces will result in a change in momentum, so no conservation 1.Force added in 2.Force removed 5.4 Conservation of Linear Momentum Shuttle Launch
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5.5 Inelastic Collisions
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Inelastic collision – two objects collide and stick together Momentum is conserved Energy is not conserved 5.5 Inelastic Collisions
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Example: On a touchdown attempt, a 95 kg running back runs toward the end zone at 3.75 m/s. A 111kg linebacker moving at 4.10 m/s meets the runner in a head on collision. If the two players stick together what is their velocity immediately after the collision? 5.5 Inelastic Collisions
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Example: In a ballistic pendulum, a 100g bullet is fired at a velocity of 200 m/s at the bob of a pendulum. The bob has a mass of 10 kg. After the collision, the object and the bob stick together and swing through an arc. How high does it get? This is first a conservation of momentum problem (how fast does the combination of bullet and bob go after the collision) Then it is a conservation of energy problem. 5.5 Inelastic Collisions
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Example: In a ballistic pendulum, a 100g bullet is fired at a velocity of 200 m/s at the bob of a pendulum. The bob has a mass of 10 kg. After the collision, the object and the bob stick together and swing through an arc. How high does it get? 5.5 Inelastic Collisions
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If the collision occurs in two dimensions We need to consider the x and y axis separately 5.5 Inelastic Collisions
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The we use vector addition to calculate the magnitude and velocity. 5.5 Inelastic Collisions
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Example: A 950kg car traveling east at 16m/s collides with a 1300 kg car traveling north at 21 m/s. If the collision is inelastic, what is the magnitude and direction of the cars after the collision? 5.5 Inelastic Collisions
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5.6 Elastic Collisions
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Elastic collision – two objects collide and bounce apart Momentum is conserved In a perfect elastic collision, energy is conserved too 5.5 Inelastic Collisions
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A 10 kg car moving at 2 m/s runs into a 5 kg car that is parked. What is the velocity of each car after the collision? 5.5 Inelastic Collisions
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A 10 kg car moving at 2 m/s runs into a 5 kg car that is parked. What is the velocity of each car after the collision? 5.5 Inelastic Collisions
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A 10 kg car moving at 2 m/s runs into a 5 kg car that is parked. What is the velocity of each car after the collision? 5.5 Inelastic Collisions
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A 10 kg car moving at 2 m/s runs into a 5 kg car that is parked. What is the velocity of each car after the collision? Confirm 5.5 Inelastic Collisions
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5.7 Center of Mass
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The point where the system can be balanced in a uniform gravitational field Uniform objects center of mass is in the center 5.7 Center of Mass Motion of CMCM Center of mass of Triangle
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Center of mass is not always in the object Objects balance if supported at their center of mass 5.7 Center of Mass
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5.8 Systems with Changing Mass: Rockets
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When a rocket is launched (or a plane takes off). Fuel is used as the rocket launches This causes the mass to decrease 5.8 Systems with Changing Mass: Rockets
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So The force due to the ejected fuel is called thrust 5.8 Systems with Changing Mass: Rockets
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In a Saturn V rocket, fuel is ejected at 13,800 kg/s and at a speed of 2440 m/s Since the initial weight of the rocket is 28,500,000N (or mass of 2,850,000 kg) 5.8 Systems with Changing Mass: Rockets
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As the rocket travels its mass drops, so the acceleration will actually increase 5.8 Systems with Changing Mass: Rockets
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