Question

A particle is dropped under gravity from rest from a height $h(g = 9.8m/s^{2})$ 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)

122.5 m

Answer 2

Distance travelled in $n$ sec = $\frac{1}{2}gn^{2}$= h .....(i)

Distance travelled in $n^{th}\sec = \frac{g}{2}(2n - 1) = \frac{9h}{25}$ .....(ii)

Solving (i) and (ii) we get. $h = 122.5m$.