Question

A body dropped from the top of the tower covers a distance $7x$ in the last second of its journey, where $x$ is the distance covered in first second. How much time does it take to reach the ground ? (in seconds)

• A. $3$
• B. $4$
• C. $5$
• D. $6$

Answer 1

The correct option is B $4$

The distance traveled in n th sec is given by $S_n=u+\frac{1}{2}(2n-1)a$

Now, $S_1=0+\frac{1}{2}(2-1)g$

or $x=g/2$ or $g=2x$ (given $S_1=x$)

So, $S_t=0+\left(1/2\right)(2t-1)g$

or $7x=\left(1/2\right)(2t-1)\left(2x\right)$

or $7=2t-1$ or $t=4sec$