So for these questions, you add if they're going in the same direction and you subtract if it's in the opposite direction for the ground observer, since the ball is moving in the opposite direction of the plane, it would be 820 km/h - 15 m/s 15 m/s * 60 s/min * 60 min/hour = 54000 m/h, 54000 m/h * 1000 m/km = 54 km/h 820 km/h - 54 km/h = 768 km/h to the ground observer By the way, I don't think it's safe for someone to throw a baseball that fast in an airplan
25. It's travelling at constant speed so acceleration is 0
d = v * t
t = d / v
t = 732 000 / 327
t= 2238.5 secs = 37.31 minutes