Problem 4.177 - Problem 4.177 [Difficulty: 3] Given: Data...

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Problem 4.177 [Difficulty: 3] Given: Data on "jet pack" rocket Find: Initial exhaust mass flow rate; mass flow rate at end; maximum time of flight Solution: Basic equation: Momentum flux in y direction Assumptions: 1) Jet pack just hovers 2) Steady flow 3) Uniform flow 4) Use relative velocities Given data V e 3000 m s = M 0 200 kg = M fuel 100 kg = g moon 0.17 g = g moon 1.67 m s 2 = At all instants, the momentum becomes M g moon v 1 m rate = V e m rate = or m rate Mg moon V e = Hence, initially m rateinit M 0 g moon V e = m rateinit 0.111 kg s = Finally, when all the fuel is just used up, the mass is M f M 0 M fuel = M f 100 kg
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