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7.31.
Model:
The two ropes and the two blocks (A and B) will be treated as particles.
Visualize:
Solve:
(a)
The two blocks and two ropes form a combined system of total mass
2.5 kg.
M
=
This combined
system is accelerating upward at
2
3.0 m/s
a
=
under the influence of a force
F
and the gravitational force
ˆ
.
Mgj
−
Newton’s second law applied to the combined system is
()
( )
net
32 N
y
FF
M
g
M
a
F
M
a
g
=− = ⇒=
+ =
(b)
The ropes are
not
massless. We must consider both the blocks and the ropes as systems. The force
F
acts only
on block A because it does not contact the other objects. We can proceed to apply the
y
component of Newton’s
second law to each system, starting at the top. Each has an acceleration
2
3.0 m/s .
a
=
For block A:
net on A
A
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This note was uploaded on 12/10/2011 for the course PHYS 1211 taught by Professor Geller during the Fall '09 term at UGA.
 Fall '09
 geller
 Mass

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