chauhan (mmc2762) – Ch1H3 – turner – (56910)
1
This
printout
should
have
27
questions.
Multiplechoice questions may continue on
the next column or page – find all choices
before answering.
001(part1of2)10.0points
Powerful sports cars can go from zero to 25
m/s (about 60 mph) in 5 seconds.
What is
the magnitude of the acceleration? Answer in
m
/
s
2
.
Correct answer: 5 m
/
s
2
.
Explanation:
To find the magnitude of a constant accel
eration, we can simply create the following
ratio:
v
final
−
v
inital
t
final
−
t
initial
=
25 m
/
s
−
0
5 s
−
0
= 5 m
/
s
2
.
002(part2of2)10.0points
How does this compare with the acceleration
of a falling rock?
1.
It is much less than the acceleration of a
falling rock.
2.
It is much greater than the acceleration
of a falling rock.
3.
The
two
accelerations
are
about
the
same.
4.
The acceleration of a falling rock increases
as it falls, so the question is not meaningful.
5.
It is about half the acceleration of a falling
rock.
correct
6.
It is about twice the acceleration of a
falling rock.
Explanation:
Objects near the surface of the earth all
fall at
g
≈
10 m
/
s
2
.
Therefore the car’s
acceleration is about half that of a falling
rock.
003(part1of2)10.0points
A tennis ball of mass 57 g travels with velocity
vectorv
i
=
(
52
,
0
,
0
)
m
/
s
toward a wall.
After bouncing off the wall,
the tennis ball is observed to be traveling with
velocity
vectorv
f
=
(−
42
,
0
,
0
)
m
/
s
.
vectorv
i
vectorv
f
Before
After
Notice that this ball only has motion in the
x
direction, so the change in momentum will
be of the form
Δ
vectorp
=
(
Δ
vectorp
x
,
0
,
0
)
.
Find Δ
vectorp
x
. Answer in kg
·
m
/
s.
Correct answer:
−
5
.
358 kg
·
m
/
s.
Explanation:
To find the change in momentum, we pro
ceed as follows:
Δ
vectorp
=
vectorp
f
−
vectorp
i
=
mvectorv
f
−
mvectorv
i
=
m
(
vectorv
f
−
vectorv
i
)
=
m
(
(−
42
,
0
,
0
)
m
/
s
− (
52
,
0
,
0
)
m
/
s)
= (0
.
057 kg)
× (−
94
,
0
,
0
)
m
/
s
=
(−
5
.
358
,
0
,
0
)
kg
·
m
/
s
.
So Δ
vectorp
x
=
−
5
.
358 kg
·
m
/
s
004(part2of2)10.0points
What is the change in the magnitude of the
tennis ball’s momentum? Answer in kg
·
m
/
s.
Correct answer:
−
0
.
57 kg
·
m
/
s.
Explanation:
Remember that magnitude refers only to
the length of a vector, not its direction. So if
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chauhan (mmc2762) – Ch1H3 – turner – (56910)
2
we want the change in magnitude, we need
to take the magnitudes of
vectorp
i
and
vectorp
f
and
find the change.
We would usually use the
Pythagorean theorem to find the magnitude
of a vector, but in this case, our vectors have
only one component each, so finding the mag
nitudes is easy. For
vectorp
i
,

vectorp
i

=

(0
.
057 kg)
× (
52
,
0
,
0
)
m
/
s

=
(
2
.
964
,
0
,
0
)
kg
·
m
/
s

= 2
.
964 kg
·
m
/
s
.
And for
vectorp
f
,
vextendsingle
vextendsingle
vectorp
f
vextendsingle
vextendsingle
=

(0
.
057 kg)
× (−
42
,
0
,
0
)
m
/
s

=
(−
2
.
394
,
0
,
0
)
kg
·
m
/
s

= 2
.
394 kg
·
m
/
s
.
So the change in magnitude is
vextendsingle
vextendsingle
vectorp
f
vextendsingle
vextendsingle
− 
vectorp
i

=
−
0
.
57 kg
·
m
/
s
.
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 Spring '11
 Antoniewicz
 Physics, Acceleration, Power, m/s, Chauhan

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