Physics 16 – Spring 2010 – Problem Set 5
5.104.
I
DENTIFY
:
The block has acceleration
, directed to the left in the figure in the problem.
Apply
to the block.
S
ET
U
P
:
The block moves in a horizontal circle of radius
. Each
string makes an angle
with the vertical.
, so
. The freebody diagram for
the block is given in Figure 5.104. Let
be to the left and let
be upward.
E
XECUTE
:
(a)
gives
.
.
(b)
gives
.
. The number of revolutions per
second is
.
(c)
If
,
and
.
.
. The number of revolutions per minute is
E
VALUATE
:
The tension in the upper string must be greater than the tension in the lower string so that
together they produce an upward component of force that balances the weight of the block.
Figure 5.104
5.115.
I
DENTIFY
:
Apply
to the circular motion of the bead. Also use Eq.(5.16) to relate
to
the period of rotation
T
.
S
ET
U
P
:
The bead and hoop are sketched in Figure 5.115a.
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The bead moves in a circle of radius
The normal force exerted on the bead by
the hoop is radially inward.
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 Spring '10
 LorenzoSorbo
 mechanics, Acceleration, Force, Frequency, Bead, freebody diagram

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