JEE Main & Advanced Physics Two Dimensional Motion Question Bank Self Evaluation Test - Motion in a Plane

  • question_answer
    Two pegs A and B thrown with speeds in the ratio 1:3 acquired the same heights. If A is thrown at an angle of \[30{}^\circ \] with the horizontal, the angle of projection of B will be

    A) \[0{}^\circ \]                

    B)        \[si{{n}^{-1}}\left( \frac{1}{8} \right)\]

    C) \[si{{n}^{-1}}\left( \frac{1}{6} \right)\]     

    D)        \[si{{n}^{-1}}\left( \frac{1}{2} \right)\]

    Correct Answer: C

    Solution :

     
    [c] \[\text{max heigth, }{{\text{H}}_{\text{A}}}=\frac{\text{u}_{\text{A}}^{2}{{\sin }^{2}}30{}^\circ }{2\text{g}};\]
    \[{{\text{H}}_{\text{B}}}=\frac{\text{u}_{\text{B}}^{2}{{\sin }^{2}}\theta }{2\text{g}}\]
    \[\text{As we know,   }{{\text{H}}_{\text{A}}}\text{=}\,\,{{\text{H}}_{\text{B}}}\text{ }\]
    \[\frac{\text{u}_{\text{A}}^{2}{{\sin }^{2}}30{}^\circ }{2\text{g}}=\frac{\text{u}_{\text{B}}^{2}{{\sin }^{2}}\theta }{2\text{g}}\]
    \[\Rightarrow \frac{{{\sin }^{2}}\theta }{{{\sin }^{2}}30{}^\circ }=\frac{\text{u}_{\text{A}}^{2}}{\text{u}_{\text{B}}^{2}}\]
    \[{{\sin }^{2}}\theta ={{\left( \frac{{{u}_{A}}}{{{u}_{B}}} \right)}^{2}}{{\sin }^{2}}30{}^\circ \Rightarrow {{\sin }^{2}}\theta =\frac{1}{36}\]
    \[\sin \theta =\frac{1}{6}\Rightarrow \theta ={{\sin }^{-1}}\left( \frac{1}{6} \right)\]


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