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Solve: (a)
gives
gives
(b)
gives
gives
(c)
gives
gives
Reflect:
In each stage the upward force is greater than the downward force, the acceleration is upward, opposite to
and the speed decreases.
5.76. Set Up:
Constant speed means
Use Newton’s 3
rd
law to relate forces on
A
and on
B
.
Solve: (a)
Treat
A
and
B
as a single object of weight
The freebody diagram for this com
bined object is given in Figure 5.76a.
gives
gives
Figure 5.76
(b)
The freebody force diagrams for blocks
A
and
B
are given in Figure 5.76b.
n
and
are the normal and friction
forces applied to block
B
by the tabletop and are the same as in part (a).
is the friction force that
A
applies to
B
. It
is to the right because the force from
A
opposes the motion of
B
.
is the downward force that
A
exerts on
B
.
is
the friction force that
B
applies to
A
. It is to the left because block
B
wants
A
to move with it.
is the normal force
that block
B
exerts on
A
. By Newton’s third law,
and these forces are in opposite directions. Also,
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This note was uploaded on 03/06/2009 for the course PHYS 114 taught by Professor Shoberg during the Spring '07 term at Pittsburg State Uiversity.
 Spring '07
 Shoberg

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