Question

A hiker stands on the edge of a cliff $490\,m$ above the ground and throws a stone horizontally with a speed of $15\,ms^{-1}$. The time taken by the stone to reach the ground is

• A. $5\,s$
• B. $10\,s$
• C. $12\,s$
• D. $15\,s$

Answer 1

Answer: (B)

$10\,s$

Answer 2

Here, $u = 15\,m \,s^{-1}$, $h = 490\,m$ Time taken by the stone to reach the ground is $t=\sqrt{\frac{2h}{g}}$ $=\sqrt{\frac{2\times490\,m}{9.8\,ms^{-2}}}$ $=10\,s$