PHY 101 1nd Edition Lecture 16 Outline of Last Lecture I Work Energy Theorem Revisited Cont II 5 6 Power III Chapter 6 Momentum Collisions IV 6 1 Momentum Impulse a Impulse Momentum Theorem b Varying Force Outline of Current Lecture V Comparison Impulse Momentum Theorem vs Work Energy Theorem VI Relationship Between Kinetic Energy Momentum Current Lecture Comparison Impulse Momentum Theorem vs Work Energy Theorem Work energy theorem o W F x KE o KE KEf KEi o KE mv2 o Unit of energy work kg m2 s2 N m o Work distance total Impulse Momentum Theorem o I F t p o p pf pi o P mv o Unit of momentum impulse Kg m s N s o Impulse time total Example Force on a golf ball o A golf ball of mass 5 x 10 2kg is struck by a club The ball leaves with a speed v 40m s o If the duration of contact time collision time is 8 x 10 4s find the average force acting on the golf ball o Solution the change in golf ball s momentum o p mvf mvi mvf o p 5 x 10 2 x 40 2 kg m s These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o Apply the impulse momentum theorem Fav t p o Fav p t 2 8 x10 4 2 x 103N 560 lb Example Crash Test o A car of mass 1 5 x 102 kg hits the wall with an initial velocity of 15m s the car rebounds with a final velocity of 2 6m s the collision time is 0 15s o 1 calculate the impulse delivered to the car o 2 average force exerted on the car during the collision Solution the change in the car s momentum p mvf mvi I fav t p 3 3 p 1 5 x 10 x 2 6 1 5 x 10 x 15 2 64 x 104 kg m s Therefore I p 2 64 x 104 kg m s o The average force exerted on the car during the collision F p t 2 64 x 104 0 15 1 76 x 105N 39 600 lb Relationship Between Kinetic Energy and Momentum Momentum p mv a vector quantity Magnitude of momentum p mv a scalar quantity Kinetic Energy Scalar o KE 1 2mv2 m2v2 2m p2 2m
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