A rocket sled accelerates from rest on a level track with negligible air and rolling resistances. The initial mass of the sled is M0 = 600 kg. The rocket initially contains 150 kg of fuel. The rocket motor burns fuel at constant rate ˙m = 15 kg/s. Exhaust gases leave the rocket nozzle uniformly and axially at Ve = 2900 m/s relative to the nozzle, and the pressure is atmospheric. Find the maximum speed reached by the rocket sled. Calculate the maximum acceleration of the sled during the run.

Answer :

xero099

Answer:

a) [tex]v \approx 834.278\,\frac{m}{s}[/tex], b) [tex]a = 96.667\,\frac{m}{s^{2}}[/tex]

Explanation:

a) The maximum speed of the rocket is given by the Tsiolkovski's Equation:

[tex]v =v_{o} - v_{ext}\cdot \ln \left(\frac{m}{m_{o}} \right)[/tex]

[tex]v = 0\,\frac{m}{s} - (2900\,\frac{m}{s} )\cdot \ln \left(\frac{450\,kg}{600\,kg} \right)[/tex]

[tex]v \approx 834.278\,\frac{m}{s}[/tex]

b) The acceleration is obtained by deriving the Tsiolkolski's Equation:

[tex]a = -v_{ext}\cdot \left(\frac{1}{m}\left) \cdot \dot m[/tex]

The maximum acceleration occured when fuel is entirely consumed. Then:

[tex]a = - \left(2900\,\frac{m}{s} \right)\cdot \left(\frac{1}{450\,kg} \right)\cdot \left(-15\,\frac{kg}{s} \right)[/tex]

[tex]a = 96.667\,\frac{m}{s^{2}}[/tex]

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