Question

freely falling body covers 7/16 of total height in the last second of the journey. find the height from
which the body is falling down (Take g= 10 ms)
​

Answer 1

80 m is the height from  which the body is falling down

Explanation:

let the time taken by the body be t , and the height from which it was thrown be h ,

now  in last second

height covered in last second   = 7 h /16

height covered in t-1 seconds = 9 h /16

let the initially body fall from rest as free falling body  ":

H = ut + 1/2 gt²

for total journey :

h   = 1/2 gt²    ....................eq 1

for t-1 second writing the equation :

9 h /16 = 1/2 g (t-1)²  .............eq 2

dividing eq 1 by eq 2

16 / 9 = (t / t-1)²

taking square root both side :

4 /3 = t/t-1

4t-4 = 3t

t = 4

using above t in eq 1

h= 1/2 * 10 * 4 * 4

= 80 m