9th Class Science Gravitation and Floatation Question Bank Gravitation

  • question_answer
    A mass M is broken in two parts : m and   (\[M-m\]) Relation between m and M so that the force of gravitation between the two parts is maximum is

    A)  \[mM=2\]                         

    B)  \[m=\frac{M}{2}\]  

    C)  \[M={{m}^{2}}\]             

    D)         none of these

    Correct Answer: B

    Solution :

    \[F=G\frac{m(M-m)}{{{r}^{2}}}=km(M-m)\] where, \[k=\frac{G}{{{r}^{2}}}\] \[\therefore \]  \[F=k\left[ \frac{{{M}^{2}}}{2}-\frac{{{M}^{2}}}{2}+mM-{{m}^{2}} \right]\]                    \[=k\left[ \frac{{{M}^{2}}}{4}-{{\left( \frac{M}{4}-m \right)}^{2}} \right]\] \[F\]is maximum, when\[\left( \frac{M}{4}-m \right)=0\] \[\Rightarrow \]               \[m=\frac{M}{2}\]


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