Question

A ball dropped from the $9^{\text{th }}$ storey of a multi-storeyed building reaches the ground in $3$ second. In the first second of its free fall, it passes through $n$ storeys, where $n$ is equal to(Take $g=10m{s}^{-2})$

• A. 1
• B. 2
• C. 3
• D. 4

Answer 1

Answer: (A)

Let the height of each storey be $y$.
$\Rightarrow$ 9th storey's height $=9y$ The ball is dropped
$\Rightarrow u=0$
$s=ut+\frac{1}{2}a{t}^2$
$9y=(0)(3s)+\frac{1}{2}\left(10m{s}^{-2}\right)(3s{)}^{2,}9y=\frac{10\times 9}{2}$
$y=5m$
In $1s,$ the ball travels, $s=\frac{1}{2}\left(10m{s}^{-2}\right)(1s{)}^2=5m$
Thus in 1 s, the ball travels 1 storey.