Thermodynamics True/False

If water, initially a superheated vapor at 30 MPa, is cooled at constant pressure, the water eventually will become saturated vapor, and then with sufficient additional cooling condensation to saturated liquid will occur

False

The change in gravitational potential energy of a 2-lb mass whose elevation decreases by 40 ft where g = 32.2 ft/s2 is -2576 ft*lbf

False

For gases modeled as ideal gases, the value of the specific heat ratio cv/cp is greater than 1

False, K=Cp/Cv > 1

The rate of heat transfer by conduction through a plane wall is greater if the wall is fabricated from plywood than from brick, assuming the same wall area and temperature gradient

False, Kplywood < Kbrick

If a system undergoes a process involving heat transfer with its surroundings but no work, that process is said to be adiabatic

False, adiabatic if no heat transfer across the boundary

The composition of a closed system cannot change

False, as long as matter stays within the boundary

According to Archimedes' principle, the magnitude of the buoyant force acting on a submerged body is equal to the weight of the body

False, buoyant force is equal to the weight of the volume displaced

Cooling of computer components achieved by a fan-induced flow of air falls in the realm of radiation heat transfer

False, cooled by convection

For heat pumps, the value of the coefficient of performance is never greater than 1

False, efficiency is always >1

Atmospheric air is normally not modeled as an ideal gas

False, it is an ideal gas

This book takes a microscopic approach to thermodynamics

False, it takes a macroscopic approach

A control volume is a special type of closed system that does not interact in any way with its surroundings

False, mass can flow to its surroundings

The total energy of a closed system can change as a result of energy transfer across the system boundary by heat and work and energy transfer accompanying mass flow across the boundary

False, mass cannot flow across boundary

A system is at steady state if no more than one of its properties changes with time

False, no properties change with time

Air always can be regarded as a pure substance

False, sometimes but no always

As a spring is compressed adiabatically, its internal energy increases

False, spring potential energy increases

A flywheel spinning owing to an input of electricity stores energy as internal energy

False, stored as KE

In this book, heat transfer to a closed system and work done on a closed system are each considered positive: Q > 0 and W > 0, respectively

False, work done on a system has negative values

A two-phase liquid-vapor pressure mixture with equal volumes of saturated liquid and saturated vapor has a quality of 50%

False, x = Mv/(Ml+Mv), x< 50%

For simple compressible systems, the state principle indicates that the number of independent intensive thermodynamics properties required to fix an intensive state is two

True

The volume of a closed system can change

True

Thermal radiation can occur in a vacuum

True

When a closed system undergoes a process between two specified states, the change in temperature between the end states is independent of details of the process

True

A refrigerant at an absolute pressure of 0.8 atm is at a gage pressure of 0.2 atm

False, 0.2 atm is the vacuum pressure

One nanosecond equals 10^9 seconds

False, 10^-9

A vessel holding 0.5 kmol of oxygen (O2) contains 16 lb of O2

False .5 mol 32 kg/kmol = 16 kg

Energy transfers by heat are induced only as a result of a temperature difference between a system and its surroundings

True

A closed system always contains the same matter; there is no transfer of matter across its boundary

True

In principle, expansion work can be evaluated using integral(p)dV for both actual and quasiequilibrium expansion processes

True

Temperature is the property that is the same for each of two systems when they are in thermal equilibrium

True

The change in specific volume from saturated liquid to saturated vapor (vg = vf) at a specified saturation pressure increases as the pressure decreases

True

The kilogram for mass and the meter for length are examples of SI base units defined relative to fabricated objects

True

The pressure unit psia indicates an absolute pressure expressed in pounds force per square inch

True

The rate of heat transfer from a hot baked potato to ambient air is greater with forced convection than natural convection

True

The change in the internal energy of a system between two states is the change in the total energy of the system between the two states less the changes of the system's kinetic and gravitational potential energies between those states

True dU=dE-dKE-dPE

1 N equals 1 kg*m/s2 but 1 lbf does not equal 1 lb*ft/s2

True, 1 lbf = 32.2 lb*ft/s^2

The Rankine degree is a smaller temperature unit that the Kelvin degree

True, 1R = .556K

Carbon dioxide (CO2) at 320 K and 55 bar can be modeled as an ideal gas

True, 320K > Tc; 55bar < Pc

The change in kinetic energy, in Btu, of a 10-lb mass whose velocity decreases from 100 ft/s to 50 ft/s is 1.5 Btu

True, KE=(1/2)(10^2 kg^2 )(100^2-50^2 m^2/s^2)(1 lbf /32.2 lb*ft/s^2)(1 Btu /778 lbf*ft) = 1.5 btu

A quasiequilibrium process for which the pressure-volume relationship is described by p/Vn = constant, where n is a constant is called a polytropic process

True, P/V^n = PV^(n-1)

For every thermodynamic cycle, the net amounts of energy transfer by heat and work per cycle are equal

True, Wcycle = Qcycle

Kinetic and potential energy are each extensive properties of a system

True, both depend on mass

Work is done by a system on its surroundings if the sole effect on everything external to the system could have been the raising of a weight

True, definition of work (F*d)

For a gas modeled as an ideal gas, cp = cv + R, where R is the gas constant for the gas

True, for ideal gases

When an ideal gas undergoes a polytropic process with n=1, the gas temperature remains constant

True, int(pdV) = mRTln(v2/v1)

Specific volume, the volume per unit of mass is an intensive property while volume and mass are extensive properties

True, intensive (independent), and extensive (dependent)

Body organs, such as the human heart, whose shapes change as they perform their normal functions can be studied as control volumes

True, mass (blood) flows across the boundary

Only changes in the energy of a system between two states have significance; no significance can be attached to the energy at a state

True, only energy of the system matter

Water at p = 100 lbf/in2 and v = 0.0169 ft3/lb is a compressed liquid

True, specific volume v=0.0169 ft^3/lb<Vf

If the value of any property of a system changes with time, that system cannot be at steady state

True, steady state means no property change with time

For ammonia at 0.45 MPa and 50 degrees C, the specific enthalpy is 1564.32 kJ/kg

True, steam tables

For liquid water, the following approximation is reasonable for many engineering calculations: v(T, p) = vl(T)

True, v varies gradually as P changes at a fixed T

The following assumptions apply for a liquid modeled as incompressible: the specific volume (density) is constant and the internal energy is a function only of temperature

True, v=constant, dU=cdT