9th Class Science Force and laws of motion Question Bank Force and Laws of Motion

  • question_answer
    A body of mass \[300\,\,g\] at rest breaks into two parts due to internal forces. One part of mass \[200\,\,g\] is found to move at a velocity of \[12\,\,m\,\,{{s}^{-1}}\] towards east. Find the velocity of the other part.

    A)  \[-24\,\,m\,\,{{s}^{-1}}\]towards west  

    B)  \[14\,\,m\,\,{{s}^{-1}}\]towards east

    C)  \[24\,\,m\,\,{{s}^{-1}}\]towards north

    D)  \[54\,\,m\,\,{{s}^{-1}}\]towards south

    Correct Answer: A

    Solution :

     According to the law of conservation of linear momentum,\[{{m}_{1}}{{u}_{1}}+{{m}_{2}}{{u}_{2}}={{m}_{1}}+{{v}_{1}}+{{m}_{2}}{{v}_{2}}\] \[\Rightarrow \]\[0={{m}_{1}}{{v}_{1}}+{{m}_{2}}{{v}_{2}},\,\,0=0.2\times 12+0.1\times {{v}_{2}}\] \[\Rightarrow \]   \[{{v}_{2}}=\frac{-0.2\times 12}{0.1}=-24\,\,m\,\,{{s}^{-1}}\] The negative sign indicates that it is moving in the opposite direction (west) with a velocity of\[-24\,\,m\,\,{{s}^{-1}}\].


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