Haryana PMT Haryana PMT Solved Paper-2011

  • 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                 \[\frac{1}{2}m2v\frac{dv}{dt}=k\]                 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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