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PROBLEM 14.98
The rocket engines of a spacecraft are fired to increase its velocity by 450 ft/s.
Knowing that 1200 lb of fuel is ejected at a relative velocity of 5400 ft/s, determine
the weight of the spacecraft after the firing.
PROBLEM 14.99
Determine the distance traveled by the spacecraft of Prob. 14.97 during the rocket
engine firing, knowing that its initial speed was 7500 ft/s and the duration of the
firing was 60 s.
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PROBLEM 14.99 (Continued)
PROBLEM 14.100
A rocket weighs 2600 lb, including 2200 lb of fuel, which is consumed at the rate of 25 lb/s and ejected with
a relative velocity of 13000 ft/s. Knowing that the rocket is fired vertically from the ground, determine (a) its
acceleration as it is fired, (b) its acceleration as the last particle of fuel is being consumed, (c) the altitude at
which all the fuel has been consumed, (d) the velocity of the rocket at that time.
PROBLEM 14.100 (Continued)
PROBLEM 14.101
Determine the altitude reached by the spacecraft of Problem 14.95 when all the fuel of its launching
rocket has been consumed.
PROBLEM 14.101 (Continued)
PROBLEM 14.102
For the spacecraft and the two-stage launching rocket of Problem 14.96, determine the altitude at
which (a) stage A of the rocket is released, (b) the fuel of both stages has been consumed.
PROBLEM 14.102 (Continued)
PROBLEM 14.103
In a jet airplane, the kinetic energy imparted to the exhaust gases is wasted as far as propelling the airplane is
concerned. The useful power is equal to the product of the force available to propel the airplane and the speed
of the airplane. If v is the speed of the airplane and u is the relative speed of the expelled gases, show that the
mechanical efficiency of the airplane is 2/( ).vu v
Explain why 1
when uv
.
