10_26_Momentum_Examples

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10/26 Momentum Examples 0 Text: Chapter7 (and 6 for Energy) 0 Presentation “Colliding Rockets” 2-D! 0 Upcoming presenters please see me 0 HW “Impulse” Due Monday 10/29 0 HW “Pendulum and Block” Due Wednesday 10/31
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Two frictionless rocket sleds are fired from rest toward each other and collide after they both burn out. They stick together after the collision. What is the final velocity of the system? v i = 0 v i = 0 m = 60kg F ?,? = 50N t = 20s (burn time) m = 30kg F ?,? = 25N t = 10s (burn time) What you know Could we use 2nd law? Energy? Momentum? Why not? Don’t know collision forces Why not? Energy not conserved F net t = p Our new friend! What is the final momentum for each before the collision after they both burn out? 1 2 1 2 p 1 = ? 1000kg m/s p f,1 = ? 1 2 1000kg m/s p i,1 = ? p i,2 = 0 p f,2 = ? p 2 = ? 250kg m/s 250kg m/s What object pushes on the rocket? What are the subscripts? F ?,? = N GAS,R v SYS,f = ?
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p 1 = ? 1000kg m/s p f,1 = ? 1 2 1000kg m/s p i,1 = 0 p i,2 = 0 p f,2 = ? p 2 = ? 250kg m/s 250kg m/s 1 2 What is the total momentum of the system before they collide? What is the total momentum of the system after they collide? p SYS = p 1 + p 2 = ? p SYS = 750kg m/s The same. No external forces so F SYS,net = 0 so p SYS = 0 What is the final velocity of the system after they collide? p
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This note was uploaded on 12/21/2010 for the course PHYS Physics 21 taught by Professor Larrywatson during the Fall '08 term at North Dakota.

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10_26_Momentum_Examples - 10/26 Momentum Examples 0 0 0 0 0...

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