Fall 2007
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Physics 105, sections 1 and 2
Exam 4
Please write your CID_____
Colton 23669
3 hour time limit.
One 3
″
×
5
″
handwritten
note card permitted (both sides). Calculators permitted. No books.
Constants/some formulas:
g
= 9.80 m/s
2
G
= 6.67
×
10
11
N
⋅
m
2
/kg
2
Mass of Sun = 1.991
×
10
30
kg
Mass of Earth = 5.98
×
10
24
kg
Radius of Earth = 6.38
×
10
6
m
Radius of Earth’s orbit = 1.496
×
10
11
m
I
pt mass
= mR
2
I
sphere
= (2/5) mR
2
I
hoop
= mR
2
I
disk
= (1/2) mR
2
I
rod
(center) = (1/12) mL
2
I
rod
(end) = (1/3) mL
2
Quadratic formula:
2
4
2
b
b
ac
x
a

±

=
Keep four significant digits throughout your calculations; do not round up to less than four.
When data is given,
assume it has at least four significant digits.
For example “15 meters” means 15.00 meters.
You are strongly encouraged to
write your work on the exam pages and circle the correct answer.
Of course also
record your final answers on the bubble sheet
.
→Write your CID above upper right corner.
Did you do this ________?
You won’t get your exam back without
writing your CID.
Problem 1. A NASA training pool filled with water is 50 m long and 50 m wide, and 4 m deep.
The
absolute
pressure at the bottom of the pool is __________ Pa.
a.
less than 109 kPa
b.
109 – 119
c.
119 – 129
d.
129 – 139
e.
More than 139 kPa
gh
P
P
ρ
+
=
0
= 1.01e5 +
1000*9.8*4 = 140200 Pa
Problem 2. The pool is now half drained, and the top half is filled with a light oil (density 400 kg/m
3
).
The
absolute
pressure at the bottom of the pool is now:
Oil and water:
1
0
1
1
2
1
2
2
2
0
1
2
P
P
gh
P
P
gh
P
P
gh
gh
ρ
ρ
ρ
ρ
=
+
=
+
=
+
+
= 1.01e5 +
400*9.8*2 +
1000*9.8*2
=
128440 Pa
1
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Problem 3. When divers come up from the bottom of the pool, they experience a buoyancy force in the oil that is
_________
the buoyancy force they felt in the water.
The density of the fluid they displace is less, so buoyant force is less.
Problem 4. Two pistons push on hydraulic fluid at rest.
The diameter of the left piston is 5 cm.
The diameter of the
right piston is 1.3 cm.
If the force on the left is 1000 N, the force on the right will be _________ N.
Pressure is constant
1
2
1
2
2
2
2
2
1
2
1
1
1000
F
F
P
A
A
A
r
F
F
A
r
=
=
=
=
1000*1.3^2/5^2 = 67.60 N
Problem 5. When an object is floating at rest, the buoyant force is _____ the object’s weight.
a.
greater than
b.
less than
c.
the same as
Choice c. (from Newton’s 2
nd
Law, object is in equilibrium)
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