A body falling under gravity covers two points A and B separated … - Vidyadip

MCQ

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 $\mathrm{g}=10 \mathrm{~ms}^{-2}$ )

A
$73$
B
$43$
C
$75$
✓
$45$

✓

Answer

Correct option: D.

$45$

d
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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