Define average velocity
2 answers:
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Let's write the equations of motion on both x- (horizontal) and y- (vertical) axis. On the x-axis, it's a uniform motion with constant velocity vx. On the y-axis, it is a uniformly accelerated motion with initial height h=90 m and acceleration of 
pointing down (so with a negative sign):
First, let's find the time at which the jumper reaches the ground. This happens when Sy(t)=0:
and so
Then, we can find the horizontal speed. In fact, we know that at the time t=4.28 s, when the jumper reached the ground, he covered exactly 180 m, so Sx=180 m. Using this into the law of motion in x, we find
First, let's find the time at which the jumper reaches the ground. This happens when Sy(t)=0:
and so
Then, we can find the horizontal speed. In fact, we know that at the time t=4.28 s, when the jumper reached the ground, he covered exactly 180 m, so Sx=180 m. Using this into the law of motion in x, we find