Question:
A person sitting on top of a tall building is dropping balls at regular intervals of one second. Find the positions of the $3^{\text {rd }}, 4^{\text {th }}$ and $5^{\text {th }}$ ball when the $6^{\text {th }}$ ball is being dropped.
Solution:
For every ball; $u=0$ and $a=g$
When $6^{\text {th }}$ ball is dropped, $5^{\text {th }}$ ball moves for 1 second, $4^{\text {th }}$ ball moves for 2 seconds, $3^{\text {rd }}$ ball moves for 3 seconds Position
$S=u t+{ }^{\frac{1}{2}} a t^{2}$
$3^{\text {rd }}$ ball $\mathrm{S}_{3}=0+\frac{1}{2}(\mathrm{~g})(3)^{2}=44.1 \mathrm{~m}$
$4^{\text {th }}$ ball $S_{4}=0+\frac{1}{2}(g)(2)^{2}=19.6 \mathrm{~m}$
$5^{\text {th }}$ ball $S_{5}=0+\frac{1}{2}(g)(1)^{2}=4.9 \mathrm{~m}$