Lecture19

Lecture19 - PHYSICS 149: Lecture 19 Chapter 7: Linear...

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PHYSICS 149: Lecture 19 • Chapter 7: Linear Momentum – 7.4 Conservation of Momentum – 7.5 Center of Mass – 7.6 Motion of the Center of Mass – 7.7 Collisions in One Dimension Lecture 19 Purdue University, Physics 149 1
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ILQ 1 Two objects with different masses have the ame kinetic energy Which has the larger same kinetic energy. Which has the larger magnitude of momentum? A) the larger mass ) e smaller mass B) the smaller mass C) they have the same momentum ) possible to tell D) impossible to tell Lecture 19 2 Purdue University, Physics 149
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ILQ 2 Is it possible for a system of two objects to have zero total momentum while having a non-zero total kinetic energy? A) Yes B) No Lecture 19 Purdue University, Physics 149 3
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Impulse and Momentum • Define Momentum –Momentum is conserved p mv = G G • Total Momentum does not change with time – Momentum is a VECTOR =- Δ p 1 Δ p 2 Δ p 1 + Δ p 2 = 0 Σ p initial = Σ p final • Define Impulse – Change in momentum requires Force acting over a time r Impulse IF t = Δ G G or Impulse Δ p = F Δ t or I = Δ p Impulse: F Δ t Vector Momentum transfer Lecture 19 Purdue University, Physics 149 4 Work: F Δ r Scalar Energy transfer
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Newton’s Second Law F ma = G G G G av p F t Δ = Δ G 0 lim t p F t Δ→ Δ = Δ G G 0 lim t p F t Δ = Δ G Lecture 19 Purdue University, Physics 149 5
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Conservation of Momentum Nf N f f Ni N i i ext v m v m v m v m v m v m G G G G G G G + + + = + + + = 2 2 1 1 2 2 1 1 then , 0 F If Momentum is a vector quantity, so both the magnitude and the direction of the total momentum at the beginning and end of the interaction must be the same. • The total momentum of a system is the vector sum of the omentum of each object in the system. momentum of each object in the system. • Internal interactions do not change the total momentum of a system. External interactions can change the total momentum of a system (recall .) Lecture 19 6 Purdue University, Physics 149
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ILQ Maggie drops a stuffed bear over the side of her crib. It hits the floor with speed v and comes to rest. She then drops a rubber ball with the same mass from the same height, and it bounces back upwards with speed v . Compare the change in the momenta of the bear and the ball. a) Δ p bear = Δ p ball b) Δ p bear = 2 Δ p ball c) Δ p bear = ½ Δ p ball d) Δ p bear = – Δ p ball Lecture 19 7 Purdue University, Physics 149
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ILQ Maggie drops a stuffed bear over the side of her crib. It hits the floor with speed v and comes to rest. She then drops a rubber ball with the same mass from the same
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Lecture19 - PHYSICS 149: Lecture 19 Chapter 7: Linear...

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