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7th Class Science Related to Competitive Exam Question Bank Work and energy

  • question_answer
    DIRECTIONS: On the basis of following diagram/ picture answer the questions given below: A small wooden box of mass 1 kg is placed on a big wooden box of mass 2 kg. The big box is moving on a smooth surface with a constant. Velocity 2 m/sec. The K.E. possessed by this system is (Assume there is no frictional force between the surfaces)

    A) 4J                               

    B) 8J

    C) 6J                   

    D) 12J

    Correct Answer: C

    Solution :

         \[K.E.=\frac{1}{2}m{{v}^{2}}\]             \[\text{Mass of system = M+m=2+1=3kg}\]             \[\text{K}\text{.E}\text{.=}\frac{1}{2}\times 3\times {{2}^{2}}\]             \[=6J\]


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