Question

A body falling freely from rest covers $\frac{7}{16}$ of the total height in the last second of its fall. What is the height from which it falls?

• A. $24.2m$
• B. $40m$
• C. $80m$
• D. $46.8m$

Answer 1

The correct option is C $80m$

The body falls through

$H=h-\frac{7h}{16}$$=\frac{9h}{16}$ during $(n-1)$ seconds and fall through ${}^{\prime }{h}^{\prime }$ in $n$ seconds

using $s=ut+1/2a{t}^2$

$\frac{9h}{16}=5(n-1{)}^2$

and $h=5n^2$

dividing$\frac{9}{16}=\frac{(n-1{)}^2}{n^2}$

we get $n=4$

Therefore $h=5\times 4^2=16\ast 5=80m$

Hence option C is correct.