CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2009

  • question_answer
    An \[\alpha \]-particle of mass \[6.4\times {{10}^{-27}}kg\] and charge \[3.2\times {{10}^{-19}}C\] is situated in a uniform electric field of \[1.6\times 10s\text{ }V{{m}^{-1}}\]. The velocity of the particle at the end of \[2\times {{10}^{-2}}m\] path when it starts from rest is

    A)  \[2~\sqrt{3}\times {{10}^{5}}m{{s}^{-1}}\]         

    B)  \[8\times {{10}^{5}}m{{s}^{-1}}\]

    C)  \[16\times {{10}^{5}}m{{s}^{-1}}\]         

    D)  \[4\times {{10}^{5}}m{{s}^{-1}}\]

    Correct Answer: D

    Solution :

    Given, \[{{m}_{\alpha }}=6.4\times {{10}^{-27}}kg\], \[{{q}_{\alpha }}=3.2\times {{10}^{-19}}C,\,E=1.6\times {{10}^{5}}V{{m}^{-1}}\] Force on a-particle                 \[F={{q}_{\alpha }}E=3.2\times {{10}^{-19}}\times 1.6\times {{10}^{5}}\]                                 \[=51.2\times {{10}^{-15}}N\] Now, acceleration of the particle                 \[\alpha =\frac{F}{{{m}_{\alpha }}}=\frac{51.2\times {{10}^{-15}}}{6.4\times {{10}^{-27}}}\]                                 \[=0.8\times {{10}^{13}}m{{s}^{-2}}\] \[\therefore \] Initial velocity, \[u=0\] \[\therefore \]  \[{{v}^{2}}=2\alpha S\]                 \[=2\times 8\times {{10}^{12}}\times 2\times {{10}^{-2}}\]                 \[=32\times {{10}^{10}}\] or            \[v=4\sqrt{2}\times {{10}^{5}}\,\,m{{s}^{-1}}\]


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