Modern Engineering Thermodynamics

Problems 29
14. Determine the mass of an object whose weight on the Moon,
where the local acceleration of gravity is 5.3 ft/s 2 , is 10.0
poundals in (a) lbm, (b) slugs, (c) g, and (d) kg.
15. Determine the acceleration of gravity at the location where 3.0
slugs of mass weigh 50.0 N.
16. How much does 10.0 lbm weigh on a planet where g = 322 ft/s 2 ?
17. Determine the value of g c at a location where a body with a
mass of 270. lbm weighs 195 lbf.
18. Develop a mechanical units system in which the mass is the stone,
the length is the angstrom (0.1 nm), and the time is the century.
(a) Define your own force unit and choose the magnitude of k 1 .
(b) Discuss the problems that would be encountered in
converting between your system and the SI system.
19. Develop a mechanical units system in which force (F), mass
(M ), length (L), and time (t) are independent quantities, using
the kgf (kilogram force) for F, and kgm (kilogram mass) for M,
the meter for L, the second for t, and 9.81 kgm·m/(kgf·s 2 )asg c .
Note the similarities between this units system (which is used
by some European engineers today) and the Engineering English
units system.
20. Develop an FLt mechanical units system in which g c = 1 and the
force is the pound force (lbf), the length is the foot, and time is
the second. Define the mass in this system to be the pound mass
(lbm) and determine the conversion between the primary units
(lbf, ft, and s) and the secondary mass (lbm) unit at standard
gravity. Note that this is not the same FLMt system used in the
Engineering English units system shown in Table 1.2. Explain the
differences and similarities between these two systems.
21. Determine the mass of 18 lbm of water in (a) lbmoles,
(b) gmoles, (c) kgmoles, and (d) slug moles.
22. How many kgmoles of nitroglycerine C 3 H 5 (NO 3 ) 3 are contained
in 1.00 kg?
23. How many lbmoles of TNT (trinitrotoluene) C 7 H 5 (NO 2 ) 3 are
contained in a 1.00 lbm stick?
24. How many lbm are contained in 1.00 lbmole of glucose C 6 H 12 O 6 ?
25. Determine the mass in lbm of 1.00 lbmole of Illinois coal
having a molecular structure of C 100 H 85 S 2.1 N 1.5 O 9.5 .
26. What will 3.0 kgmoles of CO 2 weigh at standard gravity in
(a) N, and (b) lbf?
27. Determine the molecular mass of a substance for which
5.0 gmoles weighs 10. × 10 3 dynes at standard gravity.
28. Create an absolute temperature scale based on Reaumur’s
relative temperature scale defined in Table 1.1, and name it after
you. Determine the boiling point of water in your new scale,
and the conversion factors between your scale and the Kelvin
and Rankine scales.
29. Create an absolute temperature scale based on Newton’s relative
temperature scale defined in Table 1.1, and name it after you.
Determine the boiling point of water in your new scale, and the
conversion factors between your scale and the Kelvin and
Rankine scales.
30. Both the numerical value and dimensions of the universal gas
constant R in the ideal gas formula p∀ = nRT depend on
whether the temperature T is in Kelvin or Rankine absolute
temperature units. In 1964, at Washington University, St. Louis,
Missouri, Professor John C. Georgian recognized that, if the
universal gas constant were set equal to unity and made
dimensionless, then the ideal gas equation of state could be
used to define an absolute temperature unit in terms of the
traditional mass, length, and time dimensions from the
result: T = pV/n, where p is the absolute pressure, V is the total
volume, n = m/M is the number of moles, and m and M are
mass and molecular mass, respectively.
a. Using T = pV/n (i.e., set R = 1), determine the equivalent
Georgian temperature unit in terms of the standard SI units
(m, kg, s). Call this new temperature unit the georgian, G.
b. Find the conversion factor between G and the SI units
system absolute temperature scale unit, K.
c. Find the conversion factor between G and the Engineering
English units system absolute temperature scale unit, R.
d. Determine the triple and boiling points of water in G
(Figure 1.27).
FIGURE 1.27
Problem 30, part d.
31. Show that (4πε 0 )(c 2 × 10 –7 )=1C 2 /(kg·m), where c is the
velocity of light = 2.998 × 10 8 m/s, and C is the charge in
coulomb (1C =1A·s).
32. Show that ε 0 μ 0 c 2 =1.0,whereε 0 is the electric permittivity of a
vacuum = 8.8542 × 10 –12 A 2·s 4 /(kg·m 3 ), and μ 0 = the magnetic
permeability of a vacuum = 4π × 10 –7 kg·m/(A·s) 2 .
33. If the pressure inside an automobile tire is 32.0 psig in
Engineering English units, what is its pressure in SI units?
34. If your mass is 183 lbm in the Engineering English units system,
what is your weight in (a) the Engineering English units system
and (b) the SI units system?
35. If you weigh 165 lbf in the Engineering English units system,
determine your mass in the following units systems:
(a) Engineering English, (b) SI, and (c) Technical English.
36.* The potential of a typical storm cloud can be as high as
10 9 volts. When lightning is produced, a typical lightning strike
can produces an electric current of 20,000 amps (Figure 1.28).
a. Determine the power contained in a lightning strike (in kW).
I = 20,000 amps
FIGURE 1.28
Problem 36.
10 9 volts