First slide

Release from certain height

Question

A body falling from a high Minaret travels 40 m in the last 2 seconds of its fall to ground. Height of Minaret in metre is (Take, $g = 10 {ms}^{- 2}$ )

Moderate

A

60
B

45
C

80
D

50

Solution

Let height of Minaret be H and body take time T to fall from top to bottom.
$H = \frac{1}{2} {gT}^{2}$ …(i)
In last 2 s, body travels distance of 40 m, so in $(T - 2)$ second, distance travelled $= (H - 40) m$
$\Rightarrow$ $(H - 40) = \frac{1}{2} g (T - 2)^{2}$ …(ii)
By solving Eqs. (i) and (ii), we get
T = 3 s and H = 45 m

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