ch7 - CHAPTER 7 IMPULSE AND MOMENTUM CONCEPTUAL QUESTIONS...

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CHAPTER 7 IMPULSE AND MOMENTUM CONCEPTUAL QUESTIONS 2. REASONING AND SOLUTION Since linear momentum is a vector quantity, the total linear momentum of any system is the resultant of the linear momenta of the constituents. The people who are standing around have zero momentum. Those who move randomly carry momentum randomly in all directions. Since there is such a large number of people, there is, on average, just as much linear momentum in any one direction as in any other. On average, the resultant of this random distribution is zero. Therefore, the approximate linear momentum of the Times Square system is zero. ______________________________________________________________________________________ ______ 4. REASONING AND SOLUTION a. If a single object has kinetic energy, it must have a velocity; therefore, it must have linear momentum as well. b. In a system of two or more objects, the individual objects could have linear momenta that cancel each other. In this case, the linear momentum of the system would be zero. The kinetic energies of the objects, however, are scalar quantities that are always positive; thus, the total kinetic energy of the system of objects would necessarily be nonzero. Therefore, it is possible for a system of two or more objects to have a total kinetic energy that is not zero but a total momentum that is zero. ______________________________________________________________________________________ ______ 15. REASONING AND SOLUTION For a system comprised of the three balls, there is no net external force. The forces that occur when the three balls collide are internal forces. Therefore, the total linear momentum of the system is conserved. Note, however, that the momentum of each ball is not conserved. The momentum of any given ball will change as it interacts with the other balls; the momentum of each ball will change in such a way as to conserve the momentum of the system. It is the momentum of the system of balls, not the momentum of an individual ball, that is
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ch7 - CHAPTER 7 IMPULSE AND MOMENTUM CONCEPTUAL QUESTIONS...

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