ouseph (jao888) – HW06 – tsoi – (92940)
1
This printout should have 22 questions.
Multiplechoice questions may continue on
the next column or page – fnd all choices
beFore answering.
001 (part 1 of 2) 10.0 points
A record has an angular speed oF 19 rev
/
min.
What is its angular speed?
Correct answer: 1
.
98968 rad
/
s.
Explanation:
Let :
ω
= 19 rev
/
min
.
ω
= (19 rev
/
min)
p
2
π
rad
rev
Pp
1 min
60 s
P
=
1
.
98968 rad
/
s
.
002 (part 2 of 2) 10.0 points
Through what angle does it rotate in 0
.
94 s?
Correct answer: 1
.
8703 rad.
Explanation:
Let :
t
= 0
.
94 s
.
θ
=
ω t
= (1
.
98968 rad
/
s) (0
.
94 s)
=
1
.
8703 rad
.
003 (part 1 of 2) 10.0 points
A racing car travels on a circular track oF
radius 310 m, moving with a constant linear
speed oF 70
.
9 m
/
s.
±ind its angular speed.
Correct answer: 0
.
22871 rad
/
s.
Explanation:
Let :
v
= 70
.
9 m
/
s
and
R
= 310 m
.
The linear speed is
v
=
R ω
ω
=
v
R
=
70
.
9 m
/
s
310 m
=
0
.
22871 rad
/
s
.
004 (part 2 of 2) 10.0 points
±ind the magnitude oF its acceleration.
Correct answer: 16
.
2155 m
/
s
2
.
Explanation:
With the car moving at a constant speed,
there is no tangential acceleration, so the ac
celeration is purely radial:
a
r
=
v
2
R
=
(70
.
9 m
/
s)
2
310 m
=
16
.
2155 m
/
s
2
.
005
10.0 points
Initially a wheel rotating about a fxed axis at
a constant angular deceleration oF 0
.
6 rad
/
s
2
has an angular velocity oF 0 rad
/
s and an
angular position oF 9
.
5 rad.
What is the angular position oF the wheel
aFter 2
.
9 s?
Correct answer: 6
.
977 rad.
Explanation:
Let :
α
=
−
0
.
6 rad
/
s
2
,
ω
0
= 0 rad
/
s
,
θ
0
= 9
.
5 rad
,
and
t
= 2
.
9 s
.
±rom kinematics,
θ
=
ω
0
t
+
1
2
αt
2
+
θ
0
= (0 rad
/
s) (2
.
9 s)
+
1
2
(
−
0
.
6 rad
/
s
2
) (2
.
9 s)
2
+ 9
.
5 rad
=
6
.
977 rad
.
006 (part 1 of 2) 10.0 points
A dentist’s drill starts From rest. AFter 1
.
28 s
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2
of constant angular acceleration it turns at a
rate of 20240 rev
/
min.
Find the drill’s angular acceleration.
Correct answer: 1655
.
88 rad
/
s
2
.
Explanation:
Let :
t
= 1
.
28 s
and
ω
f
= 20240 rev
/
min
.
Since
ω
0
= 0,
α
=
ω
f
−
ω
0
t
=
ω
f
t
=
20240 rev
/
min
1
.
28 s
·
2
π
rev
·
1 min
60 s
=
1655
.
88 rad
/
s
2
.
007 (part 2 of 2) 10.0 points
Throughout what angle does the drill rotate
during this period?
Correct answer: 1356
.
5 rad.
Explanation:
θ
=
ω
0
t
+
1
2
α t
2
= 0 +
1
2
(1655
.
88 rad
/
s
2
) (1
.
28 s)
2
=
1356
.
5 rad
.
008
10.0 points
An automobile moves at constant speed
down one hill and up another hill along the
smoothly curved surface as shown below.
car
Which of the following diagrams best rep
resents the directions of the velocity and the
acceleration of the automobile at the instant
that it is at the lowest position as shown?
1.
v
a
correct
2.
v
a
3.
v
a
4.
v
a
5.
v
a
Explanation:
At the lowest position, the instantaneous
velocity of the automobile is directed horizon
tally to the right.
Since the speed of the automobile is un
changed, there is no tangential accelera
tion. Also since the path of the automobile
is curved, there is centripetal acceleration,
pointing upward.
009 (part 1 of 5) 10.0 points
A car travels at a speed of 22 m
/
s around a
curve of radius 42 m.
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 Summer '08
 Staff
 Physics, Force, Friction, Correct Answer, racing car

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