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

  • question_answer
    The position of a projectile launched from the origin at \[t=0\]is given by \[\vec{r}=(40\hat{i}+50\hat{j})m\] at 2s. If the projectile was launched at an angle \[\theta \] from the horizontal, then \[\theta \] is (take \[\text{g = 10 m}{{\text{s}}^{-2}}\])

    A) \[{{\tan }^{-1}}\frac{2}{3}\]   

    B)        \[{{\tan }^{-1}}\frac{3}{2}\]

    C) \[{{\tan }^{-1}}\frac{7}{4}\]   

    D)        \[{{\tan }^{-1}}\frac{4}{5}\]

    Correct Answer: C

    Solution :

    [c] From question,
    Horizontal velocity (initial), \[{{\text{u}}_{\text{x}}}\text{=}\frac{\text{40}}{\text{2}}\text{=20 m/s}\]
    Vertical velocity (initial),\[\text{50=}{{\text{u}}_{\text{y}}}\text{t+}\frac{\text{1}}{\text{2}}\text{g}{{\text{t}}^{\text{2}}}\]
    \[\Rightarrow {{\text{u}}_{\text{y}}}\times 2+\frac{1}{2}\left( -10 \right)\times 4;\text{ or, }{{\text{u}}_{y}}=\frac{70}{2}=35\text{ m/s;}\]
    \[\therefore \tan \theta =\frac{{{\text{u}}_{\text{y}}}}{{{\text{u}}_{\text{x}}}}=\frac{35}{20}=\frac{7}{4}\Rightarrow \text{ Angle}\,\,\theta \,\text{=}\,\,\text{ta}{{\text{n}}^{-1}}\frac{7}{4}\]


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