1. you throw a ball from a window at a velocity of 2 m/s downward. how fast will the ball be
moving when it hits the sidewalk 2.5 m below?

Explanation:

Initial velocity (u) = 2 m/s

Displacement (s) = 2.5 m

Acceleration due to gravity(a)=9.81m/s^2

Final velocity (v) = ?

Now, formula is given by

v² = u² + 2×a×s

v² = 2² + 2×9.81×2.5

v² = 4 + 49.05

v² = 53.05

v = √53.05

v = 7.3 m/s

3. dark matter

empty space could also be a simple vacuum