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JEE Mains · Physics · STD 11 - Motion in straight line
  • JEE Mains 2024
  • Hard
  • Numerical

A body falling under gravity covers two points \(A\) and \(B\) separated by \(80 \mathrm{~m}\) in \(2 \mathrm{~s}\). The distance of upper point A from the starting point is________ \(\mathrm{m}\) (use \(\mathrm{g}=10 \mathrm{~ms}^{-2}\) )

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Verified Solution

Answer & Solution

Correct Answer

(D) \(45\)

Step-by-step Solution

Detailed explanation

From \(A \rightarrow B\)

\( -80=-\mathrm{v}_1 \mathrm{t}-\frac{1}{2} \times 10 \mathrm{t}^2 \)

\( -80=-2 \mathrm{v}_1-\frac{1}{2} \times 10 \times 2^2 \)

\( -80=-2 \mathrm{v}_1-20 \)

\( -60=-2 \mathrm{v}_1 \)

\( \mathrm{v}_1=30 \mathrm{~m} / \mathrm{s}\)

From \(\mathrm{O}\) to \(\mathrm{A}\)

\( \mathrm{v}^2=\mathrm{u}^2+2 \mathrm{gS} \)

\( 30^2=0+2 \times(-10)(-\mathrm{S}) \)

\( 900=20 \mathrm{~S} \)

\( \mathrm{~S}=45 \mathrm{~m}\)

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