BCECE Engineering BCECE Engineering Solved Paper-2006

  • question_answer
    In the first second of its flight, rocket ejects 1/60 of its mass with a velocity of \[2400\,\,m{{s}^{-1}}\]. The acceleration of the rocket is:

    A)  \[19.6\,m{{s}^{-2}}\]                                    

    B)         \[30.2\,m{{s}^{-2}}\]

    C)         \[40\,m{{s}^{-2}}\]                                        

    D)         \[49.8\,\,m{{s}^{-2}}\]

    Correct Answer: C

    Solution :

    Thrust force on the rocket \[{{F}_{t}}={{v}_{r}}\left( -\frac{dm}{dt} \right)\]                 or            \[ma={{v}_{r}}\left( -\frac{dm}{dt} \right)\] where\[{{v}_{r}}\]is the exhaust velocity of gases and \[-\frac{dm}{dt}\]is the mass of the ejected per unit time. Given, \[{{v}_{r}}=2400\,m{{s}^{-1}},-\frac{dm}{dt}=\frac{1}{60}kg/s,\] \[m=1\,kg\] Substituting the values in above relation \[1\times a=2400\times \frac{1}{60}\]             or                \[a=40\,m{{s}^{-2}}\]


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