A) \[24.2\,\,m\]
B) \[38.4\,\,m\]
C) \[78.4\,\,m\]
D) \[46.8\,\,m\]
Correct Answer: C
Solution :
Total height\[\Rightarrow h=\frac{1}{2}g{{n}^{2}}\], In the last second, the body covers \[\frac{7}{16}th\] of the total height. So,\[{{S}_{n}}=\frac{7}{16}h\] We have\[{{S}_{n}}=u+a\left[ n-\frac{1}{2} \right]\] Here, \[u=0\]and\[a=g\]. So,\[{{S}_{n}}=g\left[ n-\frac{1}{2} \right],\,\,{{s}_{n}}=\frac{7}{16}h\pi \frac{7}{16}\left[ \frac{1}{2}g{{n}^{2}} \right]\] \[\therefore \]\[\frac{7}{16}\left[ \frac{1}{2}g{{n}^{2}} \right]=g\left[ n-\frac{1}{2} \right]\Rightarrow n=4\,\,S\] So\[,\]\[h=\frac{1}{2}\times 9.8\times {{4}^{2}}=78.4\,\,m\].
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