Step-by-step explanation:
Dropped ball height is given by
h = 10 - 1/2 at^2
Thrown ball height is given by
h = 10 t - 1/2 at^2
when are the two h's equal ?
10 - 1/2 at^2 = 10t - 1/2 at^2
10 = 10 t
t = 1 second is the time when the heights are equal:
at one second the dropped ball is
10 - ( 1/2 *9.81*1^2) = 5.095 m high
as a check: the thrown ball is
10 (1) - 1/2 *9.81 *1^2 = 5.095 m