If a piece of wood dropped from a tall building has reached a velocity of 68.6m/s for how long has it been falling

Given that,

Let initial speed of the piece of wood, u = 0

Finally, it reaches to a speed of 68.6 m/s. It will be its final velocity. We need to find the time taken by it to fall. Using equation of motion as :

a = g

So, it will taken 7 seconds to fall. Hence, this is the required solution.

grav potential energy