Question

A boy on a cliff 49m high drops a stone 1 second later he throws a second stone after the first they both hit the ground at same time with what speed did he throw the second stone

Answer 1

For first stone

h = 49m
g = 9.8m/s²
t = ?
u = 0

apply
h = ut + gt²/2
49 = 0 + 9.8t²/2
t² = 10
t = √10 = 3.16s

for second stone
t = 3.16 - 1 = 2.16s
h = 49m
g = 9.8m/s²
u = ?

again apply
h = ut + gt²/2
49 = u*2.16 + 9.8*2.16²/2
49 = 2.16*u + 22.86
26.14/2.16 = u
u = 12.10m/s