Question

A body falls freely from the top of a tower. It covers $36\%$ of the total height in the last second before striking the ground level. The height of the tower is

• A. 50m
• B. 75m
• C. 100m
• D. 125m

Answer 1

Answer: (D)

Let height of tower is h and body takes time t to reach the ground when it falls freely.
$\therefore h=\frac{1}{2}g{t}^2\dots$(i)
In last second ie, the sec body travels $=0.36h$
It means in rest of the time ie, in $(t-1)\sec$
it travels $=h-0.36h=0.64h$
Now, applying equation of motion for $(t-1)\sec$
$0.64h=\frac{1}{2}g(t-1{)}^2\dots$ (ii)
From Eqs. (i) and (ii), we get
$t=5s$ and $h=125m$