huynh (hph268) – HW #1 – clark – (56485)
1
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beFore answering.
001
10.0 points
Consider the expression 2
π
r
ℓ
g
,
where
ℓ
is
length and
g
is gravitational acceleration in
units oF length divided by time squared.
Evaluate its units.
1.
s
correct
2.
m
3.
s
m
4.
m
2
5.
m
s
6.
s
2
7.
p
m
s
P
2
8.
p
s
m
P
2
Explanation:
[
ℓ
] = m
and [
g
] =
m
s
2
.
2 and
π
are constants, so
r
[
ℓ
]
[
g
]
=
R
m
÷
m
s
2
=
R
m
·
s
2
m
=
√
s
2
= s
.
002
10.0 points
A graph oF a straight line going through two
points is shown below.
b
b
y

5

3

1 0 1 2 3 4 5
x

5

4

3

2

1
0
1
2
3
4
5
What is the equation oF this line?
1.
y
= +
2
9
x
+
8
9
2.
y
=

9
2
x
+
8
9
3.
y
=

2
9
x
+ 4
4.
y
=

9
2
x

8
9
5.
y
= +
2
9
x
+ 4
6.
y
= +
2
9
x

8
9
correct
7.
y
= +
9
2
x

4
8.
y
=

2
9
x

8
9
9.
y
= +
2
9
x

4
10.
y
= +
9
2
x

8
9
Explanation:
Let :
(
x
1
, y
1
) = (

5
,

2)
(
x
2
, y
2
) = (4
,
0)
.
The slope is
m
=
(0)

(

2)
(4)

(

5)
= +
2
9
.
Using 2 points
(
y

y
1
) =
m
(
x

x
1
)
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View Full Documenthuynh (hph268) – HW #1 – clark – (56485)
2
y
=
m
(
x

x
1
) +
y
1
,
so
y
= +
2
9
(
x
+ 5)

2
= +
2
9
x

8
9
.
003
(part 1 of 2) 10.0 points
Consider two planets with uniform mass dis
tributions. The mass density and the radius
of planet 1 are
ρ
1
and
R
1
, respectively, and
those of planet 2 are
ρ
2
and
R
2
What is the ratio
M
1
M
2
of their masses?
1.
M
1
M
2
=
p
ρ
1
ρ
2
Pp
R
1
R
2
P
3
correct
2.
M
1
M
2
=
p
ρ
1
ρ
2
R
2
R
1
P
3
3.
M
1
M
2
=
p
ρ
2
ρ
1
R
1
R
2
P
4.
M
1
M
2
=
p
ρ
2
ρ
1
R
1
R
2
P
2
5.
M
1
M
2
=
p
ρ
2
ρ
1
R
1
R
2
P
3
6.
M
1
M
2
=
p
ρ
2
ρ
1
R
2
R
1
P
3
7.
M
1
M
2
=
p
ρ
1
ρ
2
R
1
R
2
P
2
8.
M
1
M
2
=
p
ρ
1
ρ
2
R
2
R
1
P
2
9.
M
1
M
2
=
p
ρ
2
ρ
1
R
2
R
1
P
2
10.
M
1
M
2
=
p
ρ
1
ρ
2
R
1
R
2
P
Explanation:
ρ
=
m
V
,
so
M
1
M
2
=
ρ
1
p
4
3
π R
3
1
P
ρ
2
p
4
3
π R
3
2
P
=
ρ
1
R
3
1
ρ
2
R
3
2
.
004
(part 2 of 2) 10.0 points
What is the ratio
A
1
A
2
of the circular areas
deFned by the two equators?
1.
A
1
A
2
=
p
R
2
R
1
P
2
2.
A
1
A
2
=
π
p
R
1
R
2
P
3
3.
A
1
A
2
=
π
p
R
1
R
2
P
2
4.
A
1
A
2
=
p
R
1
R
2
P
3
5.
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 Spring '11
 Zao
 Physics, Orders of magnitude, 1.0 mm, 1.87 km, 1.865 km

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