11/10/22, 10:41 PM Aerodynamics Objective Questions and Answers - Sanfoundry

Aerodynamics Questions and Answers – The

This set of Aerodynamics Objective Questions & Answers focuses on “The Basic Normal Shock
Equations – 2”.

1. For a non-perfect gas, if we double the pressure while keeping the temperature same, the speed
of sound remains the same.
a) False
b) True
View Answer

Answer: a
Explanation: For a non-perfect gas, the speed of sound is a pressure of temperature and pressure
(or density). And hence, by changing the pressure, while keeping the temperature constant, speed
of sound changes.

2. For a perfect gas, if we half the density, keeping the temperature same the speed of sound
changes. This is due to the change in pressure.
a) True
b) False
View Answer

Answer: b
Explanation: The given statement is false. For a perfect gas, the speed of sound is a pressure of
temperature only. And hence, by changing pressure or density but keeping the temperature
same, speed of sound will not change.

3. The isothermal compressibility is given as___________

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c) 1

γp

d)
ρ

View Answer

Answer: b
Explanation: The isothermal compressibility differs from the isentropic compressibility by a factor
of gamma. The isothermal compressibility is given as τt= while the isentropic compressibility is
1

given as τs= 1

γp
.

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4. Which is not the correct reason for sound of speed being higher in helium than in air at the same
temperature?
a) γ for helium is higher than air
b) Gas constant is same for both
c) Helium is lighter than air
d) R for helium is much larger than for air
View Answer

Answer: b
Explanation: The sound of speed depends on gamma, T and the gas constant R for the respective
gas. In case of helium and air, the gamma for helium is higher than air. Also, helium is lighter than
air thus, R for helium being higher. This gives, at the same temperature, speed of sound more in
helium than air.

5. The correct statement for a point where the speed of sound is a, is_______
a) a* is the stagnation speed of sound
b) a* is the maximum speed of sound
c) a0 is the characteristic speed of sound
d) a0 is the stagnation speed of sound
View Answer

Answer: d
Explanation: For a point in the flow, where the speed of sound is a, a0 is the stagnation speed of
sound associated with that point. While a* is the sonic characteristic value associated with that
same point. None of these is the maximum speed of sound in the flow.

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11/10/22, 10:41 PM Aerodynamics Objective Questions and Answers - Sanfoundry

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6. The incorrect relation for properties associated with the flow, for a point in the flow where the
speed of sound is a, is_______
2

a*2=
a
a) ≠const
γ+1 0

2(γ−1) γ−1

b) a*2=const
γ+1

2(γ−1)
2
a
c) γ−1
0
=const
2

a*2=
a
d) =const
γ+1 0

2(γ−1) γ−1

View Answer

Answer: a
Explanation: The two properties, a* and a0, of the flow are related to each other by the relation:
2

a*2=
a
. These two (a* and a0) are defined quantities and are constant at a point in the
γ+1 0

2(γ−1) γ−1
2

a*2=
a
flow. Thus, the correct relation is =const, since gamma is also a constant.
γ+1 0

2(γ−1) γ−1

7. Select the incorrect statement for the properties concerned with a flow.
a) a* and a0 are constant at a point
b) a* and a0 are constant along the streamline for an adiabatic, inviscid, steady flow
c) a* and a0 are constant along the entire flow for an adiabatic, inviscid, steady flow
d) a* and a0 are related but not equal
View Answer

Answer: c
Explanation: a* and a0 are the defined properties of the flow, constant at a point. They are related
to each other but not same. For an adiabatic, inviscid, steady flow they are constant along the
streamline. And if all the streamlines are coming from same uniform free-stream, they are
constant along the entire flow.

8. For a calorically perfect gas, the ratio of stagnation to static temperature depends upon_______
a) γ
b) γ , M
c) M
d) R, M
View Answer

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11/10/22, 10:41 PM Aerodynamics Objective Questions and Answers - Sanfoundry

Answer: b
Explanation: The stagnation and static temperatures for a calorically perfect gas are related with
the equation =1+ M2. Thus, it is clearly seen that this ratio depends on the gamma and the
T0 γ−1

T 2

Mach number in the medium. It’s a very important relationship.

9. The definitions of P0 and ρ0 involve______

Answer: b
Explanation: The defined properties of the flow P0 and ρ0 involve isentropic compression, which is
adiabatic and reversible both. These properties are the values of the flow parameters when the
flow is isentropically compressed to zero velocity, at a point with properties P and ρ.

10.The properties of a flow with subscript * denotes M=1. Which of these is the correct ratio for a
flow with gamma= 1.4?
∗

a) T
=0.528
T0
∗

b) P

P0
=0.833
∗

c) ρ

ρ0
=0.634
d) Data inadequate
View Answer

Answer: c
Explanation: The defined flow properties are related to each other with relations involving only
Mach number and gamma. Hence, when these two values are given, the ratios can be calculated.
These are important ratios and for M=1 and gamma=1.4 the values are =0.833, =0.528,
∗ ∗
T P

T0 P0
∗
ρ

ρ0
=0.634

11. The characteristic Mach number is constant for a given value of temperature and gamma.
a) False
b) True
View Answer

Answer: a
Explanation: The defined M* or the characteristic Mach number depends upon the Mach number,
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for any given gamma. It changes if the Mach number is changed, which changes by changing the
flow speed at any temperature. Hence, the given statement is false.

12. The characteristic Mach number and Mach number are related. Which of these is not correct?
a) M=1, M*=1
b) M<1, M*<1
c) M<1, M*<1
d) M→∞, M*→0
View Answer

Answer: d
Explanation: The characteristic Mach number and the Mach number behave almost in a similar
pattern. The only difference if when the Mach number tends to infinity, the characteristic Mach
number tends to a finite value. This finite value depends only on gamma is never zero.

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