Final answer:
The horizontal component of the initial velocity of the shell is 450 m/s, while the vertical component is 0 m/s.
Step-by-step explanation:
Given that the military jet is flying horizontally with a velocity of 450 m/s, the horizontal component of the initial velocity of the shell will also be 450 m/s. This is because the shell is fired horizontally from the artillery gun and will have the same initial velocity as the jet in the horizontal direction. The horizontal component of the initial velocity of the shell is 450 m/s, while the vertical component is 0 m/s.
Since the jet is 20,000 m above the ground, the vertical component of the initial velocity of the shell will be 0 m/s. This is because the shell is fired horizontally and doesn't have any initial vertical velocity. The only force acting on the shell is gravity, pulling it downwards.