BHU PMT BHU PMT (Mains) Solved Paper-2008

  • question_answer
    If force (F), work (W) and velocity (v) are taken as fundamental quantities, then the dimensional formula of time (T) is

    A)  \[[WFv]\]                          

    B)  \[[WF{{v}^{-1}}]\]

    C)  \[[{{W}^{-1}}{{F}^{-1}}v]\]                         

    D)  \[[W{{F}^{-1}}{{v}^{-1}}]\]

    Correct Answer: D

    Solution :

                     Let \[T\propto {{F}^{a}}{{W}^{b}}{{v}^{c}}\]                         ...(i) \[[T]={{[ML{{T}^{-2}}]}^{a}}{{[M{{L}^{2}}{{T}^{-2}}]}^{b}}{{[L{{T}^{-1}}]}^{c}}\] \[[{{T}^{1}}]=[{{M}^{a+b}}][{{L}^{a+2b+c}}][{{T}^{-2a-1b-c}}]\] Comparing the powers, we get \[a+b=0\]                              ...(ii) \[a+2b+c=0\]                       ...(iii) \[-2a-2b-c=1\]               ...(iv) Solving Eqs. (ii), (iii) and (iv), we get \[a=-1,b=1,c=-1\] Therefore, from Eq. (i), \[[T]=k[{{F}^{-1}}{{W}^{-1}}{{v}^{-1}}]\] Taking\[k=1\]in SI system, we have                 \[[T]=k[W{{F}^{-1}}{{v}^{-1}}]\]


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