Browse Questions

# A freely falling body is found to cover $7/16 ^{th}$ of the height of fall during the last second of its motion.Find the height from which it falls $(g=10m/s^2)$

$(a)\; 50 m \quad (b)\;80 m \quad (c)\;120 m \quad (d)100 m$

The body falls through
$h-\bigg(\large\frac{7h}{16} \bigg)=\frac{9h}{16}$ during $(n-1)$ seconds and fall through 'h' in n seconds
using $s=ut+\large\frac{1}{2}$$at ^2 \large\frac{9h}{16}$$=5(n-1)^2$
and $h=5n^2$
dividing $\large\frac{9}{16}=\frac{(n-1)^2}{n^2}$
we get $n=4$
Therefore $h=5 \times 4^2=80 m$
Hence b is the correct answer.

edited Jan 25, 2014 by meena.p