Answer:
t = 3.44 s
Explanation:
We are given;
Fired from rest, and so; u = 0 m/s
Final speed; v = 170 m/s
Height above flat ground; y_o = 58 m
Height at starting point; y = 0 m
Thus, from Newton's equation of motion, we have;
y - y_o = ut - ½gt²
(since it's motion is against gravity)
Plugging in the relevant values, we have;
0 - 58 = 0 - (½ × 9.8 × t²)
-58 = -4.9t²
t² = 58/4.9
t = √(58/4.9)
t = 3.44 s
