Question 1

The mean free path where commercial aircraft fly (about 30,000 ft) is nearest:
A) 0.0076 mm
B) 0.0026 mm
C) 0.00076 mm
D) 0.00016 mm

Accepted Answer

$0.00076 \mathrm {~mm}$
$$\begin{aligned}
\lambda & = 0.225 \frac { \mathrm { m } } { \rho d ^ { 2 } } \
& = 0.225 \frac { 4.8 \times 10 ^ { - 26 } \mathrm {~kg} } { ( 0.00089 \times 515.4 ) \mathrm { kg } / \mathrm { m } ^ { 3 } \times \left( 3.7 \times 10 ^ { - 10 } \right) ^ { 2 } \mathrm {~m} ^ { 2 } } = \underline { 1.72 \times 10 ^ { - 7 } \mathrm {~m} }
\end{aligned}$$
The factor $515.4$ came from Table A.1 in the Appendix. ×

Question 2

If force was selected as a fundamental dimension rather than mass, the units on density would be: 
A) $\mathrm { kg } / \mathrm { m } ^ { 3 }$
B) $\mathrm { N } \cdot \mathrm { s } ^ { 2 } / \mathrm { m } ^ { 4 }$
C) $\mathrm { N } / \mathrm { s } ^ { 2 } \cdot \mathrm { m } ^ { 2 }$
D) $\mathrm { s } ^ { 2 } / \mathrm { N } \cdot \mathrm { m } ^ { 2 }$

Accepted Answer

$\mathrm { N } \cdot \mathrm { s } ^ { 2 } / \mathrm { m } ^ { 4 }$
$[ \rho ] = [ \mathrm { m } ] / [ V ] = \left( F \cdot T ^ { 2 } / L \right) / L ^ { 3 } = F \cdot T ^ { 2 } / L ^ { 4 }$. Using SI units, this is $\underline { \mathrm { N } \cdot \mathrm { s } ^ { 2 } / \mathrm { m } ^ { 4 } }$

Question 3

The fluids that are considered in this text:
A) Have relatively low viscosities
B) Must be subjected to a normal stress to have motion
C) Have molecules that move relatively slowly
D) Move when subjected to any shear stress

Accepted Answer

Move when subjected to any shear stress
The fluids of interest in Fluid Mechanics always move when subjected to a shearing
stress no matter how small that shearing stress may be.

Question 4

Which of the following is not acceptable in the SI system of units?
A) $\mathrm { N } \cdot \mathrm { cm } / \mathrm { s }$
B) $\mathrm { kg } / \mathrm { L }$
C) $\mathrm { m } / \mathrm { ns }$
D) $\mathrm { J } / \mathrm { m } ^ { 2 }$

Accepted Answer

$\mathrm { N } \cdot \mathrm { cm } / \mathrm { s }$
$\mathrm { cm }$ is only allowed when used as $\mathrm { cm } , \mathrm { cm } ^ { 2 }$, or $\mathrm { cm } ^ { 3 }$

Question 5

The energy usage in the United States in 2010 was about 100 × 1018 J. This can be written as:
A) 100 million GJ
B) 1000 million GJ
C) 100 billion MJ
D) 100 trillion MJ

Accepted Answer

100 trillion $\mathrm { MJ }$
A trillion is $10 ^ { 12 }$. So, $100 \times 10 ^ { 12 } \times 10 ^ { 6 } \mathrm {~J} = \underline { 100 \times 10 ^ { 18 } \mathrm {~J} }$

Quiz 1: Basic Considerations

The mean free path where commercial aircraft fly (about 30,000 ft) is nearest:

If force was selected as a fundamental dimension rather than mass, the units on density would be:

The fluids that are considered in this text:

Which of the following is not acceptable in the SI system of units?

The energy usage in the United States in 2010 was about 100 × 1018 J. This can be written as: