An object takes 5 s to fall to the ground from a height of 5 m on a certain planet, starting from rest. The value of $g$ on that planet is:

1. For free fall from rest, $s = \dfrac{1}{2}gt^2$ with $u = 0$. 2. Substitute $s = 5$ m and $t = 5$ s: $5 = \dfrac{1}{2}g(5)^2$. 3. So $5 = \dfrac{1}{2}g \times 25 = 12.5\,g$. 4. $g = \dfrac{5}{12.5} = 0.4$ m/s$^2$; 10 m/s$^2$ is Earth's value and is the trap. _Source: Balbharati (Maharashtra Board) Class 10 Science & Technology, Ch 1 "Gravitation", p.24_