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

  • question_answer
    The work down in time t on a body of mass m which is accelerated from rest to a speed \[{{v}_{1}}\] in time \[{{t}_{1}}\] as a function of time t is given by

    A)  \[\frac{1}{2}m\frac{{{\upsilon }_{1}}}{{{t}_{1}}}{{t}^{2}}\]           

    B)         \[m\frac{{{\upsilon }_{1}}}{{{t}_{1}}}{{t}^{2}}\]

    C)  \[\frac{1}{2}{{\left( \frac{m{{\upsilon }_{1}}}{{{t}_{1}}} \right)}^{2}}{{t}^{2}}\]   

    D)         \[\frac{1}{2}m{{\frac{{{\upsilon }_{1}}}{{{t}_{1}}}}^{2}}{{t}^{2}}\]  

    Correct Answer: D

    Solution :

     Work done\[=F\times S=ma\times a{{t}^{2}}=\frac{1}{2}m{{a}^{2}}{{t}^{2}}\] Now, acceleration, \[a=\] rate of change in speed\[=\frac{{{V}_{1}}}{{{t}_{1}}}\] Substituting, it in the above equation, we have work done\[=\frac{1}{2}m{{\left( \frac{{{V}_{1}}}{{{t}_{1}}} \right)}^{2}}{{t}^{2}}\]


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