JEE Main & Advanced Physics Two Dimensional Motion JEE PYQ - Two Dimensional Relative Motion

  • question_answer
    The position of a projectile launched from the origin at t = 0is given by \[\vec{r}=\left( 40\hat{i}+50\hat{j} \right)m\]at \[t=2s.\]If the projectile was launched at an angle \[\theta \] from the horizontal, then \[\theta \] is (take \[g=10\,m{{s}^{-2}}\]) [JEE ONLINE 09-04-2014]

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

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

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

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

    Correct Answer: C

    Solution :

    [c] From question, Horizontal velocity (initial),
    \[{{u}_{x}}=\frac{40}{2}=20m/s\]
    Vertical velocity (initial), \[50={{u}_{y}}t+\frac{1}{2}g{{t}^{2}}\]
    \[\Rightarrow \]\[{{u}_{y}}\times 2+\frac{1}{2}(-10)\times 4\]or\[50=2{{u}_{y}}-20\]
    or\[{{u}_{y}}=\frac{70}{2}=35m/s\]
    \[\therefore \]\[\tan \theta =\frac{{{u}_{y}}}{{{u}_{x}}}=\frac{35}{20}=\frac{7}{4}\]\[\Rightarrow \]
    Angle\[\theta ={{\tan }^{-1}}\frac{7}{4}\]
    \[\therefore \]\[\frac{\sin {{\theta }_{c}}}{\sin {{\theta }_{s}}}=\frac{\frac{5}{7}g}{\frac{2}{3}g}=\frac{15}{14}\]


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