This set of Astronautics Multiple Choice Questions & Answers (MCQs) focuses on “Aerodynamic Forces”.
1. Our atmosphere has the highest density of air at ____________
a) mean sea level
b) the outermost layer
c) intermediate layers
d) ground level
View Answer
Explanation: The atmosphere is the huge envelope of air that surrounds our planet. At ground level, this air is being crushed by all the layers above it and therefore exhibits the highest density just on top of Earth’s terrain.
2. The innermost layer of Earth’s atmosphere is called the
a) stratosphere
b) troposphere
c) mesosphere
d) thermosphere
View Answer
Explanation: The first layer of Earth’s atmosphere starting from the bottom is called the troposphere. It extends from the ground up to an altitude of 10 to 12 kilometers.
3. Climbing higher and higher, the density of the atmosphere remains constant.
a) True
b) False
View Answer
Explanation: As one goes higher and higher, the atmosphere becomes less dense. This is because at greater altitudes, the air is not being crushed by as much quantity of air compared to lower heights. As we reach the edge of the atmosphere, there is virtually no air above us, meaning that this layer contains an extremely low density of molecules.
4. The drag on an object moving through the atmosphere is due to the object’s ___________
a) mass
b) density
c) velocity
d) color
View Answer
Explanation: An object based on Earth is literally immersed within a gigantic ocean of air (which we call ‘the atmosphere’). While the object moves, there must always be some resistance to its motion (similar to the opposing force experienced when a skydiver deploys a parachute in order to slow down) caused by moving against all this surrounding air. If the object speeds up, the amount of airflow against the object will increase and the greater the resistive force becomes.
5. The drag on an object of frontal area ‘A’ moving with a speed ‘v’ through a fluid of density ‘ρ’ is given by
a) D = \(\frac{1}{2}\)ρvA CD
b) D = \(\frac{1}{2}\)ρv2A CD
c) D = ρv2A CD
d) D = \(\frac{1}{2}\)ρv2A2 CD
View Answer
Explanation: Say an object translates through a fluid (like air) of density ‘ρ’ exposing a frontal area ‘A’ against the fluid while moving with a velocity ‘v’. The drag on the object is then D = \(\frac{1}{2}\)ρv2A CD where ‘CD’ is called the coefficient of drag of the object.
6. Looking at the equation D = \(\frac{1}{2}\)ρv2A CD we see that the drag on an object depends on the altitude above the Earth at which it moves.
a) True
b) False
View Answer
Explanation: The drag on an object depends on the density of the fluid through which it moves. The density of the atmosphere changes with altitude (being the highest near the surface and continually decreasing with height) and so the drag on an object must change with height (given a fixed velocity ‘v’).
7. Atmospheric drag on satellites is noticeably felt only at _____ altitudes.
a) Geostationary Earth Orbit
b) Geosynchronous Earth Orbit
c) Low Earth Orbit
d) Medium Earth Orbit
View Answer
Explanation: Our atmosphere lies relatively close to Earth and the motion of LEO satellites is constantly opposed by the sparsely populated air molecules spread across the outermost layer of Earth’s atmosphere.
8. Perturbations from atmospheric drag are secular in nature.
a) True
b) False
View Answer
Explanation: Atmospheric drag persists for as long as the satellite is in motion around the Earth and acts continuously on the orbiter, making it a secular perturbation effect.
9. What is the effect of atmospheric drag on a satellite?
a) Lowers the orbital height
b) Increases the satellite’s lifespan
c) Increases the orbital height
d) Deforms the satellite
View Answer
Explanation: Atmospheric drag acts continuously on a satellite and always opposes its forward motion, thereby snapping energy out of the orbit and lowering the satellite’s altitude.
10. For an elliptical orbit, the drag force causes ___________
a) a decrease in orbital energy
b) an increase in orbital energy
c) a decrease in eccentricity
d) an increase in eccentricity
View Answer
Explanation: Consider an elliptical orbit around Earth. As the satellite passes near the Earth (i.e., through the perigee), atmospheric drag opposes the motion of the satellite, causing it to climb to an apogee height which is lower than that of its previous pass. Over time, this phenomenon causes a continuous reduction in the apogee accompanied by a slightly lower reduction in the perigee (since the atmospheric drag at apogee is comparatively lesser than that at perigee), which results in a decreasing eccentricity.
Sanfoundry Global Education & Learning Series – Astronautics.
To practice all areas of Astronautics, here is complete set of Multiple Choice Questions and Answers.
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