A stone is thrown upward from a roof at the same time as another, identical stone is dropped from there. The two stones
a.have the same speed when they reach the ground
b.none of the above
c.reach the ground at the same time
d. have the same acceleration when they reach the ground
a.have the same speed when they reach the ground
b.none of the above
c.reach the ground at the same time
d. have the same acceleration when they reach the ground