Question

A stone is dropped from $25\text{th}$ storey of a multistorey building and reaches the ground in $5\text{s}$. How many storey of the building will the stone cover in first second, if the height of each storey is same?
(Take $g=10m/s^2$)

• A. $1$
• B. $2$
• C. $3$
• D. $5$

Answer 1

The correct option is A $1$

Let height of single storey is $h$, then total height from where stone was dropped, $H=25h$
Given, $u=0,a=g,s=H,t=5$
Therefore, using $s=ut+\frac{1}{2}a{t}^2$
$\Rightarrow H=0\times t+\frac{1}{2}g{t}^2$
$\Rightarrow 25h=\frac{1}{2}\times 10\times 5^2$
$\Rightarrow h=5\text{m}$
So, height of one storey is $5\text{m}$
Now, distance travelled in $1\text{s}$$=ut+\frac{1}{2}a{t}^2$
$=0+\frac{1}{2}g\times 1^2$
$=5\text{m}$
Therefore stone will pass through one storey in first second.
(A) option is correct