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.
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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.
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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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 Spring '09
 DARICI
 Force, Impulse And Momentum, Momentum, Vfb

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