Question

A paper weight is dropped from the roof of a block of multistorey flats, each storey being $3$ meters high. It passes the ceiling of the ${20}^{th}$ storey at $30$ $m/s$. If $g=10m/s^2$, how many storey does the flat have?

• A. 25
• B. 30
• C. 35
• D. 40

Answer 1

Answer: (C)

35

$v^2=u^2+2gs$
$\Rightarrow (30{)}^2=0^2+2\times 10\times s$

$s=\frac{900}{20}=45m$
$\Rightarrow$ It has travelled $\frac{45}{3}=15$ storeys
And it is ${21}^{st}$ storey from bottom.

Hence, total storeys $=20+15=35$ storeys.