if a block of wood drooped from a tall building has attained a velocity of 78.4 m/s, how long has it been falling?

Answer 1

Assuming no air resistance, falling objects accelerate at the rate of 9.8 m/s/s.

If the object has attained a velocity of 78.4 m/s, it would have fallen 78.4/9.8 = 8 seconds.