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PHY2004 Lectures 1-20

# PHY2004 Lectures 1-20 - PHY 2004 Lectures 16-20 MOMENTUM...

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PHY 2004 Lectures 16-20 MOMENTUM Collision Impulse I = F t F=ma=m(V f -V I )/t Hence: I = mV f - mV i Momentum P = mV NO impulse, no force, no collision NO CHANGE IN MOMENTUM called conservation of momentum

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Example: You jump off a boat Before jump P=0 Therefore, after jump P=0 P after = P Man + P boat Therefore P boat = -P man = -400 = M boat V boat = 60 V boat THUS V boat = - 6.7 m/s (minus sign means goes backward)
ELASTIC COLLISIONS Momentum initial = Momentum after M 1 V 1 Init + M 2 V 2 Init = M 1 V 1 after + M 2 V 2 after No energy losses, therefore (1/2)M 1 (V 1 Init ) 2 + (1/2)M 2 (V 2 Init )2 = (1/2)M 1 (V 1 after ) 2 + (1/2)M 2 (V 2 after ) 2 USE both equations can show; V 1 Init + V 1 after = V 2 Init + V 2 after USED often Collisions in TWO Dimensions Separate momentum into components in X and Y direction P total in X direction is constant AND P total in Y direction is constant

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Chapter 9 ANGULAR MEASUREMENTS In time t sweep out s r is in RADIANS 1 Revolution = 360 degrees =2 radians ANGULAR VELOCITY = /t radians / sec.
TANGENTIAL VELOCITY V T = r r must be in radians /sec. V T is in m/s if r is in meters ------------------------------------------------------------------------------------ CENTRIPETAL ACCELERATION Tangential velocity is CONSTANT in magnitude BUT direction changes by V THEREFORE there is an acceleration toward the center a C = V T 2 /r

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PLANETS Constant angular speed (approximately) Centripetal acceleration = V T 2 /r Provided by gravitational force F=GMm/r 2 HENCE V T = (GM/r)
PHY 2004 LECTURES 10-12 EQUILIBRIUM Chapter 8. No motion ( OR constant motion i.e. no acceleration) Vector sum of forces =0 I.e. in figure to right F 1 + F 2 = F UP In figure below, Equilibrium requires For horizontal direction; T1 = T2 cos 53 = 0.6T2 For vertical direction; T2 sin53 =2 00, OR 0.8T2 =200

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