NEET NEET SOLVED PAPER 2013

  • question_answer
    When a proton is released from rest in a room, it starts with an initial acceleration \[{{a}_{0}}\] towards west. When it is projected towards north with a speed \[{{\upsilon }_{0}}\] it moves with an initial acceleration\[3{{a}_{0}}\]towards west. The electric and magnetic fields in the room are

    A) \[\frac{m{{a}_{0}}}{e}west,\frac{2m{{a}_{0}}}{e{{v}_{0}}}up\]

    B) \[\frac{m{{a}_{0}}}{e}west,\frac{2m{{a}_{0}}}{e{{v}_{0}}}dwon\]

    C) \[\frac{m{{a}_{0}}}{e}east,\frac{3m{{a}_{0}}}{e{{v}_{0}}}up\]

    D) \[\frac{m{{a}_{0}}}{e}east,\frac{3m{{a}_{0}}}{e{{v}_{0}}}down\]

    Correct Answer: B

    Solution :

    Initial acceleration,\[{{a}_{0}}=\frac{eE}{m}\] ?(i) \[\Rightarrow \]\[E=\frac{{{a}_{0}}m}{e}\therefore \frac{e{{v}_{0}}B+eE}{m}=3{{a}_{0}}\] Or \[e{{v}_{0}}B+eE=3{{a}_{0}}m\] \[\therefore \]\[e{{v}_{0}}B=3m{{a}_{0}}-eE\] \[\Rightarrow \] \[=3m{{a}_{0}}-m{{a}_{0}}\][from eq. (1)] \[\Rightarrow \] \[e{{v}_{0}}B=2m{{a}_{0}}\] \[\therefore \] \[B=\frac{2m{{a}_{0}}}{e{{v}_{0}}}\]


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