roofner (bar784) – Homework 13 – Weathers – (17104)
1
This printout should have 13 questions.
Multiplechoice questions may continue on
the next column or page – Fnd all choices
before answering.
001
10.0 points
The speed of a moving bullet can be deter
mined by allowing the bullet to pass through
two rotating paper disks mounted a distance
77 cm apart on the same axle.
±rom the
angular displacement 15
.
5
◦
of the two bul
let holes in the disks and the rotational speed
1201 rev
/
min of the disks, we can determine
the speed of the bullet.
15
.
5
◦
v
1201 rev
/
min
77 cm
What is the speed of the bullet?
Correct answer: 357
.
975 m
/
s.
Explanation:
Let :
ω
= 1201 rev
/
min
,
d
= 77 cm
,
and
θ
= 15
.
5
◦
.
θ
=
ω t
t
=
θ
ω
,
so the speed of the bullet is
v
=
d
t
=
d ω
θ
=
(77 cm) (1201 rev
/
min)
15
.
5
◦
×
360
◦
1 rev
1 m
100 cm
1 min
60 s
=
357
.
975 m
/
s
.
keywords:
002
10.0 points
A wheel starts from rest at
t
= 0 and rotates
with a constant angular acceleration about a
Fxed axis. It completes the Frst revolution in
5
.
5 s.
How long after
t
= 0 will the wheel com
plete the second revolution?
Correct answer: 7
.
77817 s.
Explanation:
Let :
t
1
= 5
.
5 s
,
θ
1
= 1 rev
,
and
θ
2
= 2 rev
.
The wheel starts from rest, so
θ
=
θ
0
+
1
2
αt
2
=
1
2
α t
2
∝
t
2
.
Thus
θ
2
θ
1
=
t
2
2
t
2
1
t
2
=
r
θ
2
θ
1
t
1
=
r
2 rev
1 rev
(5
.
5 s)
=
7
.
77817 s
.
003
10.0 points
A bicycle is turned upside down while its
owner repairs a ²at tire. A friend spins the
other wheel of radius 0
.
4 m and observes that
drops of water ²y o³ tangentially. She mea
sures the height reached by drops moving ver
tically. A drop that breaks loose from the tire
on one turn rises 66
.
4 cm above the tangent
point. A drop that breaks loose on the next
turn rises 63
.
4 cm above the tangent point
(the angular speed of the wheel is decreas
ing).
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View Full Documentroofner (bar784) – Homework 13 – Weathers – (17104)
2
h
0
.
4 m
radius
ω
Find the angular deceleration of the wheel.
The acceleration of gravity is 9
.
8 m
/
s
2
.
As
sume the angular deceleration is constant.
Correct answer: 29
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 Fall '08
 Weathers
 mechanics, Work, Moment Of Inertia, Correct Answer, kg, θ

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