Question

A body falling from a high minaret travels 40 m in the last 2 s of its fall to ground. Height of minaret is [Take $g = 10 \,m \,s^{-2}$]

• A. 60 m
• B. 45 m
• C. 80 m
• D. 50 m

Answer 1

Answer: (B)

45 m

Answer 2

Let h be total height and t be the total time of flight. Then, $h = \frac{1}{2}? 10 ? t^{2} = 5t^{2}\quad\cdots\left(i\right)$ and $h - 40 = \frac{1}{2} ? 10 ?\left( t - 2\right)^{2} = 5\left(t^{2} + 4 - 4t\right)$ Using $\left(i\right)$, we get $5t^{2} - 40 = 5\left(t^{2} - 4 - 4t\right)$ or $5t^{2} - 40 = 5t^{2} + 20 - 20t$ or $20t = 60$ or $t = 3\, s$ $\therefore\quad h = 5\left(3\right)^{2} = 45 \,m$