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JEE Mains · Physics · STD 11 - Motion in plane
  • JEE Mains 2014
  • Hard
  • MCQ

The initial speed of a bullet fired from a rifle is \(630\, m/s\). The rifle is fired at the centre of a target \(700\, m\) away at the same level as the target. How far above the center of the target (in \(m\)) the rifle must be aimed in order to hit the target? (Take \(g=10 \;m/s^2\))

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Answer & Solution

Correct Answer

(C) \(6.17\)

Step-by-step Solution

Detailed explanation

\(\begin{array}{l}
Let\,'t'\,be\,the\,\,time\,taken\,by\,the\,bullet\,\,to\,hit\,the\,{\rm{target}}{\rm{.}}\\
\therefore \,{\rm{700 = }}\,{\rm{m = 63}}{{\rm{0}}^{ - 1}}t\\
 \Rightarrow t = \frac{{700m}}{{630m{s^{ - 1}}}} = \frac{{10}}{9}\sec \\
For\,velrtical\,motion,\\
Here,\,u = 0\\
\therefore \,h = \frac{1}{2}g{t^2}
\end{array}\)

\(\begin{array}{l}
 = \frac{1}{2} \times 10 \times {\left( {\frac{{10}}{9}} \right)^2}\\
 = \frac{{500}}{{81}}m = 6.17\,m\\
Therefore,\,the\,rifle\,must\,be\,{\rm{aimed}}\,{\rm{6}}{\rm{.17}}\,{\rm{m}}\,{\rm{above}}\,{\rm{the}}\,{\rm{center}}\,{\rm{of}}\,{\rm{the}}\,\\
{\rm{target}}\,{\rm{to}}\,{\rm{hit}}\,{\rm{the}}\,{\rm{target}}{\rm{.}}\,
\end{array}\)

 

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