Question

A body dropped from the top of a tower cover a distance $9x$ in the last second of its journey where $x$ is the distance covered in the first second. How much time does it take to reach the ground?

• A. $3sec$
• B. $4sec$
• C. $5sec$
• D. $6sec$

Answer 1

Answer: (C)

$5sec$

Given:
$\overrightarrow{s}$ in the first second $=x$
$\overrightarrow{s}$ in the last second $=9x$
$s=ut+\frac{1}{2}9t^2$
$x=0+\frac{1}{2}\times 10\times 1^2=5x$
$\therefore 9x=45m$
$45=V\left(1\right)+\frac{1}{2}\times 10(1{)}^2$
$\Rightarrow V\left(1\right)=40m/s$
$v=u+at=0+10\left(t\right)$
$\Rightarrow t=4s$
Total time of fall $=(4+1)sec=5sec$