wo stones are dropped from top of tower a half a second apart.the time after dropping the first stone at which the distance between two stones is 20m is

if first block travels for t time then second travels for (t- 1/2)s

  h₁=5t²                      taking g =10

h₂ = 5 (t - 1/2)²       substracting

20 = 5(t - 1/4)

or t= 4.25s

As intial velocity is 0.

distance travelled by 1st stone for t seconds is S= 1/2 t²

distance travelled by 2nd stone is S= 1/2 (t-(1/2))²   { since 2nd body is throwned after 1/2 second}

and separation is 20 m

therefore;

                      [1/2 t²] - [ 1/2  (t-(1/2))² ] = 20

                       implies t=4.25 seconds