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  3. 9th Class
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  5. Work and energy

9th Class Science Work and energy Question Bank Work Power and Energy Conceptive Objective Problems

  • question_answer
    An outfielder throws baseball with an initial kinetic energy of 8000J. An infielder at the same level catches the ball when its kinetic energy is 4000J. If the distance between them is 200m, the resistance of the air is

    A)  100 N                   

    B)  50 N

    C)  20 N     

    D)  200 N

    E)  None

    Correct Answer: C

    Solution :

      Given initial \[K.E.\,=8000\,\,J\] Final \[K.E.\,=4000\,\,J\] \[S=200\,\,mF=?\] Change in \[K.E.\,=4000\,\,J\] According to Work - energy theorem, Change in K.E. = Work done \[\therefore \,\,4000\,\,J=W\] \[400J=F\times S(\because W=F\times S)\] \[\Rightarrow F=\frac{4000}{200}=20N\]              


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