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BHU PMT BHU PMT (Mains) Solved Paper-2011

  • question_answer
    If M is the mass of rocket, r is rate of ejection of gases and u is velocity of gases with respect to rocket, then acceleration of the rocket\[\frac{dv}{dt}\]is equal to

    A)  \[\frac{ru}{(M-rt)}\]                     

    B)  \[\frac{(M-rt)}{ru}\]

    C)  \[\frac{ru}{(M-rt)}\]                     

    D)  \[\frac{ru}{M}\]

    Correct Answer: A

    Solution :

                     Here, initial mass of rocket\[M=\frac{dM}{dt}=r\] Relative velocity of gas w.r.t. rocket\[=u\] So, acceleration of the rocket \[a=\frac{F}{m}=\frac{u\left( \frac{dm}{dt} \right)}{\left( M-\frac{dm}{dt}\times t \right)}\] \[=\frac{ur}{M-rt}\]


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