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

  • question_answer
    A man weighing 80 kg is standing in a trolley weighing 320 kg. The trolley is resting on frictionless horizontal rails. If the man starts walking on the trolley with a speed of 1 m/s, then after 4 sec his displacement relative to the ground will be

    A)  5 m

    B)  4.8 m

    C)  3.2m  

    D)  3.0 m

    Correct Answer: C

    Solution :

     Initially momentum of the system is zero. Due to motion of man, trolley along with the man will travel in backwards direction. \[\therefore \]      \[80\times 1+(80+320)v'=0\] or         \[v'=-0.2\,\,m/s\] Man travels forward with the speed of 1 m/s and backwards with the speed of\[0.2\,\,m/s\]. So, net velocity of the man is\[0.8\,\,m/s\].             \[d=v\times t=0.8\times 4=3.2\]


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