Q98 / 200 · NEET 2011 (Screening) · Physics
A boy standing at the top of a tower of $20 \mathrm{~m}$ height drops a stone. Assuming $g=10 \mathrm{~ms}^{-2}$, the velocity with which it hits the ground is
- Correct answerA$20 \mathrm{~m} / \mathrm{s}$
- B$40 \mathrm{~m} / \mathrm{s}$
- C$5 \mathrm{~m} / \mathrm{s}$
- D$10 \mathrm{~m} / \mathrm{s}$
Solution
Given, $g=10 \mathrm{~ms}^{-2}$ and $h=20 \mathrm{~m}$
We have
$$
\begin{aligned}
V & =\sqrt{2 g h} \\
& =\sqrt{2 \times 10 \times 20}=\sqrt{400}=20 \mathrm{~ms}^{-1}
\end{aligned}
$$
Hence, the correct answer is option: 'A'.