RAJASTHAN PMT Rajasthan - PMT Solved Paper-2009

  • question_answer
    A particle of mass m is projected with a velocity v making an angle of \[45{}^\circ \] with the horizontal. The magnitude of angular momentum of the projectile about the axis of projection, when the particle is at maximum height

    A)  zero                     

    B)         \[\frac{m{{v}^{3}}}{4\sqrt{2g}}\]

    C)  \[\frac{m{{v}^{3}}}{\sqrt{2g}}\]                               

    D)         \[\frac{m{{v}^{2}}}{2g}\]

    Correct Answer: B

    Solution :

    Maximum height attained by the projectile,                 \[H=\frac{{{v}^{2}}{{\sin }^{2}}\theta }{2g}\] Here,     \[\theta ={{45}^{o}}\] \[\therefore \]  \[H=\frac{{{v}^{2}}{{\sin }^{2}}{{45}^{o}}}{2g}=\frac{{{v}^{2}}}{2g}\times {{\left( \frac{1}{\sqrt{2}} \right)}^{2}}=\frac{{{v}^{2}}}{4g}\] Velocity at maximum height\[=v\cos {{45}^{o}}=\frac{v}{\sqrt{2}}\] Angular momentum at maximum height\[=mvr\]                 \[=m\times \frac{v}{\sqrt{2}}\times \frac{{{v}^{2}}}{4g}\]                 \[=\frac{m{{v}^{3}}}{4\sqrt{2}g}\]


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