Physics Question. Pls help me out.?

3) PHYSICS Short Answer Consider a planet where g equals 5.0 meters per second squared. Ignoring friction, if an object started from rest, how far would it fall vertically off a cliff in 4.0 seconds, giving your answer in standard SI units? ANSWER: 40 METERS (must give units) (Solution: d = ½ × at2 = ½ × 5×... show more 3) PHYSICS Short Answer Consider a planet where g equals 5.0 meters per second squared. Ignoring friction, if an object started from rest, how far would it fall vertically off a cliff in 4.0 seconds, giving your answer in standard SI units?

ANSWER: 40 METERS (must give units)
(Solution: d = ½ × at2 = ½ × 5× 42 = 40 meters)

Pls explain to me how this works. BTW i am an eight grader and dont kno anything about this stuff yet.
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