WB JEE Medical WB JEE Medical Solved Paper-2011

  • question_answer
    A box is moved along a straight line by a machine delivering constant power. The distance moved by the body in time t is proportional to

    A)  \[{{t}^{\frac{1}{2}}}\]   

    B)                  \[{{t}^{\frac{3}{4}}}\]

    C)  \[{{t}^{\frac{3}{2}}}\]                                   

    D)  \[{{t}^{2}}\]

    Correct Answer: C

    Solution :

                     We are given that a box is moved along a straight line by a machine under constant power. So, we have power P = Fv = mav                                                 \[P=m\frac{dv}{dt}v\]                 or                            \[\int_{{}}^{{}}{vdv}=\int_{{}}^{{}}{\frac{P}{m}dt}\]                                                 \[\frac{{{v}^{2}}}{2}=\frac{Pt}{m}\]                 or                            \[v=\sqrt{\frac{2P}{m}t}\]                 or                            \[\frac{dx}{dt}=\sqrt{\frac{2P}{m}t}\]                                 \[\int_{{}}^{{}}{dx=\sqrt{\frac{2P}{m}}\int_{{}}^{{}}{{{t}^{1/2}}dt}}\]                                 \[x=\sqrt{\frac{2P}{m}}\frac{{{t}^{3/2}}}{3/2}\]                 \[\therefore \]  \[x\propto {{t}^{3/2}}\]


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