9th Class Science Work and energy Question Bank Work, Energy and Power

  • question_answer
    The mass of a body is increased by \[100%\] and velocity of a body is decreased by\[50%\]. What is the percentage change in its kinetic energy?

    A) \[50%\]                         

    B) \[-50%\]  

    C) \[75%\]             

    D)        \[150%\]

    Correct Answer: B

    Solution :

     Mass of body \[m+100%\]of\[m\] \[=m+\frac{100}{100}m=2\,\,m\] Velocity\[=v-\frac{50}{100}v=\frac{v}{2}\], \[K.E.=\frac{1}{2}m{{v}^{2}}\] \[K{{E}_{1}}\frac{1}{2}{{m}_{1}}v_{1}^{2}=\frac{1}{2}(2m){{\left( \frac{v}{2} \right)}^{2}}=\frac{m{{v}^{2}}}{4}=\frac{1}{2}KE\] Percentage change in             \[=KE=\frac{K{{E}_{1}}-KE}{KE}\times 100=50%\] \[\therefore \]\[KE\] of the body decreases by\[50%\]


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