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Conceptual Question about Conservation of Momentum 
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#1
May1112, 04:28 AM

P: 42

Hi,
I just want to understand this concept a bit better. The law states that momentum is conserved when there is no external force acting on the system. Now consider this situation where two cars of equal mass and moving at equal speed collide headon to come to rest. Would the momentum be conserved? Looking at the situation, there is friction acting on the cars so does that mean momentum is not conserved? Similarly for this situation: a bicycle rider ceases to pedal and her bicycle coasts along the path until it comes to rest. Is momentum not conserved as well due to friction? Many thanks. 


#2
May1112, 04:49 AM

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#3
May1112, 04:50 AM

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P: 26,157

hi jayadds!
(And angular momentum is conserved about any axis about which there is no external torque) in a collision, momentum is conserved in any direction in which there is no external impulse (and in a collision, angular momentum is conserved in any direction in which there is no external impulsive torque) friction (unlike say, a step or a barrier) is not impulsive, so you use it before and after the collision, but you ignore it for the collision itself! 


#4
May1112, 05:06 AM

P: 42

Conceptual Question about Conservation of Momentum



#5
May1112, 05:12 AM

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#7
May1312, 02:18 PM

P: 3

hi,i have the similar problem...if i include the earth in my system.EARTH HAS ZERO MOMENTUM before and after colision of car right???? then acc to conservation of momentum MV+MV=0(WHERE M IS MASS OF CAR AND V IS VELOCITY OF CARS) then V=0?????



#8
May1312, 02:29 PM

P: 132




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