Solution Manual for College Physics A Strategic Approach 3rd Edition by Knight | ISBN 0321879724

Solution Manual for College Physics A Strategic
Approach 3rd Edition by Knight | ISBN 0321879724

MOTION IN ONE DIMENSION




Q2.1. Reason: The elevator must speed up from rest to cruising velocity. In
g; g; g; g; g; g; g; g; g; g; g;


the middle will be a period of constant velocity, and at the end a period of
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slowing to a rest.
g; g; g; g;


The graph must match this description. The value of the velocity is zero at the
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beginning, then it increases, then, during the time interval when the velocity
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is constant, the graph will be a horizontal line. Near the end the graph will
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decrease and end at zero.
g; g; g; g; g;




Assess: After drawing velocity-versus-time graphs (as well as others), stop and
g; g; g; g; g; g; g; g; g; g;


think if it matches the physical situation, especially by checking end points,
g; g; g; g; g; g; g; g; g; g; g; g;


maximum values, places where the slope is zero, etc. This one passes those
g; g; g; g; g; g; g; g; g; g; g; g; g;


tests.
g;




Q2.2. Reason: (a) The sign conventions for velocity are in Figure 2.7. The
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sign conventions for acceleration are in Figure 2.26. Positive velocity in
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vertical motion means an object is moving upward. Negative acceleration
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means the acceleration of the object is downward. Therefore the upward
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velocity of the object is decreasing. An example would be a ball thrown
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upward, before it starts to fall back down. Since it’s moving upward, its
g; g; g; g; g; g; g; g; g; g; g; g; g;


velocity is positive. Since gravity is acting on it and the acceleration due to
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gravity is always downward, its acceleration is negative.
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(b) To have a negative vertical velocity means that an object is moving
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downward. The acceleration due to gravity is always downward, so it is
g; g; g; g; g; g; g; g; g; g; g; g;

, always negative. An example of a motion where both velocity and
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acceleration are negative would be a ball dropped from a height during its
g; g ; g; g; g; g; g; g; g; g; g; g; g;


downward motion. Since the acceleration is in the same direction as the
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velocity, the velocity is increasing.
g; g; g; g; g;

,
, 2-2 Chapter 2


Assess: For vertical displacement, the convention is that upward is positive and
g; g; g; g; g; g; g; g; g; g; g;


downward is negative for both velocity and acceleration.
g; g; g; g; g; g; g; g;




Q2.3. Reason: Where the rings are far apart the tree is growing rapidly. It
g; g; g; g; g; g; g; g; g; g; g; g; g;


appears that the rings are quite far apart near the center (the origin of the
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graph), then get closer together, then farther apart again.
g; g; g; g; g; g; g; g; g;




Assess: After drawing velocity-versus-time graphs (as well as others), stop and
g; g; g; g; g; g; g; g; g; g;


think if it matches the physical situation, especially by checking end points,
g; g; g; g; g; g; g; g; g; g; g; g;


maximum values, places where the slope is zero, etc. This one passes those
g; g; g; g; g; g; g; g; g; g; g; g; g;


tests.
g;




Q2.4. Reason: Call “up” the positive direction. Also assume that there is no
g; g; g; g; g; g; g; g; g; g; g; g;


air resistance. This assumption is probably not true (unless the rock is
g; g; g; g; g; g; g; g; g; g; g; g;


thrown on the moon), but air resistance is a complication that will be
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addressed later, and for s mall, heavy items like rocks no air resistance is a
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pretty good assumption if the rock isn’t going too fast. To be able to draw
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this graph without help demonstrates a good level of understanding of
g; g; g; g; g; g; g; g; g; g; g;


these concepts. The velocity graph will not go up and down as the rock
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does—that would be a graph of the position. Think carefully about the
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velocity of the rock at various points during the flight.
g; g; g; g; g; g; g; g; g; g;


At the instant the rock leaves the hand it has a large positive (up) velocity,
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so the value on the graph at t = 0 needs to be a large positive number. The
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velocity decreases as the rock rises, but the velocity arrow would still point
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up. So the graph is still above the t axis, but decreasing. At the tippy-top
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the velocity is zero; that corresponds to a point on the graph where it
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crosses the t axis. Then as the rock descends with increasing velocity (in
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the negative, or down, direction), the graph continues below the t axis. It
g; g; g; g; g; g; g; g; g; g; g; g; g;


may not have been totally obvious before, but this graph will be a straight
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line with a negative slope.
g; g; g; g; g;