A 3-kg plastic tank that has a volume of $0.2 \mathrm{~m}^3$ is filled with liquid water. Assuming the density of water is $1000 \mathrm{~kg} / \mathrm{m}^3$, determine the weight of the combined system.

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Problem 15

Determine the mass and the weight of the air contained in a room whose dimensions are $6 \mathrm{~m} \times 6 \mathrm{~m} \times 8 \mathrm{~m}$. Assume the density of the air is $1.16 \mathrm{~kg} / \mathrm{m}^3$. Answers: 334.1 kg, 3277 N

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Problem 16

At $45^{\circ}$ latitude, the gravitational acceleration as a function of elevation $z$ above sea level is given by $g=a-b z$, where $a=9.807 \mathrm{~m} / \mathrm{s}^2$ and $b=3.32 \times 10^{-6} \mathrm{~s}^{-2}$. Determine the height above sea level where the weight of an object will decrease by 1 percent. Answer: $29,539 \mathrm{~m}$

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Problem 17

A $150-\mathrm{lbm}$ astronaut took his bathroom scale (a spring scale) and a beam scale (compares masses) to the moon where the local gravity is $g=5.48 \mathrm{ft} / \mathrm{s}^2$. Determine how much he will weigh (a) on the spring scale and (b) on the beam scale. Answers: (a) 25.5 lbf ; (b) 150 lbf

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Problem 18

The acceleration of high-speed aircraft is sometimes expressed in $g$ 's (in multiples of the standard acceleration of gravity). Determine the net upward force, in N, that a $90-\mathrm{kg}$ man would experience in an aircraft whose acceleration is 6 g 's.

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Problem 19

A 5-kg rock is thrown upward with a force of

150 N at a location where the local gravitational acceleration is $9.79 \mathrm{~m} / \mathrm{s}^2$. Determine the acceleration of the rock, in $\mathrm{m} / \mathrm{s}^2$.

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Problem 20

Solve Prob. 1-19 using EES (or other) software.
Print out the entire solution, including the
numerical results with proper units.

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Problem 21

The value of the gravitational acceleration $g$ decreases with elevation from $9.807 \mathrm{~m} / \mathrm{s}^2$ at sea level to $9.767 \mathrm{~m} / \mathrm{s}^2$ at an altitude of $13,000 \mathrm{~m}$, where large passenger planes cruise. Determine the percent reduction in the weight of an airplane cruising at $13,000 \mathrm{~m}$ relative to its weight at sea level.
Modeling and Solving Engineering Problems

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Problem 22

What is the difference between precision and accuracy? Can a measurement be very precise but inaccurate? Explain.

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Problem 23

What is the difference between the analytical and experimental approach to engineering problems? Discuss the advantages and disadvantages of each approach.

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Problem 24

What is the importance of modeling in engineering? How are the mathematical models for engineering processes prepared?

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Problem 25

When modeling an engineering process, how is the right choice made between a simple but crude and a complex but accurate model? Is the complex model necessarily a better choice since it is more accurate?

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Problem 26

How do the differential equations in the study of a physical problem arise?

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Problem 27

What is the value of the engineering software packages in (a) engineering education and (b) engineering practice?

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Problem 28

Determine a positive real root of this equation using EES:

$$
2 x^3-10 x^{0.5}-3 x=-3
$$

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Problem 29

Solve this system of two equations with two
unknowns using EES:

$$
\begin{aligned}
& x^3-y^2=7.75 \\
& 3 x y+y=3.5
\end{aligned}
$$

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Problem 30

Solve this system of three equations with three unknowns using EES:

$$
\begin{aligned}
2 x-y+z & =5 \\
3 x^2+2 y & =z+2 \\
x y+2 z & =8
\end{aligned}
$$

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Problem 31

Solve this system of three equations with three unknowns using EES:

$$
\begin{aligned}
x^2 y-z & =1 \\
x-3 y^{0.5}+x z & =-2 \\
x+y-z & =2
\end{aligned}
$$

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Problem 32

The weight of bodies may change somewhat from one location to another as a result of the variation of the gravitational acceleration $g$ with elevation. Accounting for this variation using the relation in Prob. 1-16, determine the weight of an $80-\mathrm{kg}$ person at sea level $(z=0)$, in Denver ( $z=1610$ $\mathrm{m})$, and on the top of Mount Everest ( $z=8848 \mathrm{~m}$ ).

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Problem 33

A man goes to a traditional market to buy a steak for dinner. He finds a $12-\mathrm{oz}$ steak ( $1 \mathrm{lbm}=16 \mathrm{oz}$ ) for $$\$ 3.15$$. He then goes to the adjacent international market and finds a $320-\mathrm{g}$ steak of identical quality for $$\$ 2.80$$. Which steak is the better buy?

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Problem 34

The reactive force developed by a jet engine to push an airplane forward is called thrust, and the thrust developed by the engine of a Boeing 777 is about $85,000 \mathrm{lbf}$. Express this thrust in N and kgf.
Design and Essay Problem

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Problem 35

Write an essay on the various mass- and volume-measurement devices used throughout history. Also, explain the development of the modern units for mass and volume.

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