Question

an arrow is shot vertically upward 2 seconds later it is at a height of 42m with what velocity was the arrow shot, how long is the arrow in flight altogether

Answer 1

h = Vi t - 4.9 t^2
so
42 = 2 Vi -4.9*4
solve for Vi

then when is h = 0 again?
0 = Vi t - 4.9 t^2
0 = t (Vi - 4.9 t)
t = 0 at start of course
then it comes back to ground at
t = Vi/4.9