Question

A particle is dropped under gravity from rest from a height $h(g=9.8m/{\sec }^2)$ and it travels a distance $9h/25$ in the last second, the height $h$ is

• A. 100 m
• B. 122.5 m
• C. 145 m
• D. 167.5 m

Answer 1

Answer: (B)

Let $h$ distance is covered in $ns$.

$\Rightarrow h=\frac{1}{2}g{n}^2...(i)$

Distance covered in $n^{th}$ second $=\frac{1}{2}g(2n-1)$

$\Rightarrow \frac{9h}{25}=\frac{g}{2}(2n-1)...(ii)$

From $(i)$ and $(ii),h=122.5m$