JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2010

  • question_answer
        The KE of a body varies directly as the time (t) elapsed. The force acting varies directly as

    A)  \[{{t}^{-1}}\]                                    

    B)  \[{{t}^{-1/2}}\]

    C)  \[{{t}^{1/2}}\]                                  

    D)  \[t\]

    Correct Answer: B

    Solution :

                    Here, \[KE=\frac{1}{2}m{{v}^{2}}=kt\] where, k is a constant Differentiating w.r.t., t we get                 \[\frac{1}{2}m\,2v\,\frac{dv}{dt}=k\] Or           \[m\,\frac{dv}{dt}=\frac{k}{v}\] Or           \[F=\frac{k}{v}\] But           \[v=\sqrt{\frac{2kt}{m}}\] \[\therefore \]  \[F=\frac{k}{\sqrt{\frac{2kt}{m}}}\] Or           \[F\propto {{t}^{-1/2}}\]


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