# Aerodynamics Questions and Answers – Introduction to Nonequilibrium Systems

This set of Aerodynamics Multiple Choice Questions & Answers (MCQs) focuses on “Introduction to Nonequilibrium Systems”.

1. The chemical and vibrational process occur due to molecular collision.
a) True
b) False

Explanation: All the vibrational and chemical processes occur by the process of molecular collision. When the molecules collide, there is a change between the vibrational energy before and after the collision which is dependent on the temperature and kinetic energy.

2. Which of these parameters affect the number of collisions?
a) Pressure of the setup
b) Kinetic energy between the molecules
c) Density of the apparatus
d) Temperature of the apparatus

Explanation: For a molecule to become vibrationally excited, it has to undergo several number of collisions which is affected by the kinetic energy present between these colliding particles. Higher kinetic energy results in higher gas temperature which eventually leads to lesser number of collisions required for the molecule to become vibrationally excited.

3. Time taken for the number of collisions depends on which of these parameters?
a) Molecular collision frequency
b) Molar density
c) Number of moles
d) Boltzmann constant

Explanation: The amount of time taken by the molecules for collision depends on the molecular collision frequency. Thus parameter tells how many collisions take place with a neighboring particle in a second for a single particle.

4. If the temperature increases, what happens to the molecular collision frequency?
a) Increases
b) Decreases
c) No change
d) First increases then decreases

Explanation: The molecular collision frequency (Z) is given by the relation:
Z ∝ $$\frac {p}{\sqrt {T}}$$
Therefore, molecular collision frequency is inversely proportional to the square root of temperature which means that as the temperature increases, collision frequency decreases.

5. For which condition is collision theory low?
a) Low temperature and pressure
b) High temperature and pressure
c) Low temperature, high pressure
d) High temperature, low pressure

Explanation: Molecular collision frequency is directly proportional to the pressure of the molecule and inversely proportional to the square root of the temperature. Therefore, for obtaining low collision frequency, the pressure should be low and the temperature should be high.

Sanfoundry Global Education & Learning Series – Aerodynamics.

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