3241: Aerodynamics and Flight Mechanics
Name: _____Solution____
Concept Quiz #5
Consider again the example of the rocket on a thrust stand discussed in class. An actual
rocket in flight is not attached to a thrust stand and is free to rapidly accelerate through
the atmosphere and into orbit. The momentum equation complete describes this motion.
(
29
∑
∫
∫
=
⋅
+
F
dS
n
U
U
dV
U
dt
d
S
V
d
d
d
d
ˆ
ρ
ρ
Look again at the rocket on the test stand, but now assume that the test stand connection
with the rocket breaks and the rocket is free to accelerate to the left, as shown in the
drawing below:
Using the given parameters in the figure and taking a control volume that is fixed to the
rocket and accelerates with it, what is the time rate of change of momentum (first term in
the momentum equation) within the control volume?
Be careful of the signs. The velocity of the rocket, or the velocity of the control volume,
is traveling in a direction opposite to the positive xdirection associated with the sign
convention. The velocity of the control volume (or rocket) is a vector quantity and is: V
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 Spring '11
 Staff
 Acceleration, Force, General Relativity

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