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)

125m

Answer 2

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