Acceleration of rock due to gravity

[WhyDidItakeIt]

A rock is dropped from rest at the top of a cliff 125 cm high.

a) At what speed does it strike the ground?

b) How long does it take?



To find the velocity the equation used is v = u + at

I know that (u = 0) as it's from rest and g = 9.81 ms (gravity)

But I just need help on how to get the velocity when the time is not stated!

I have the answers but I'm not sure how to reach them

a) 49.5 ms

b) 5.05 ms

 

[Hootenanny]

You have two options:

(1) Use conservation of energy

(2) Use another kinematic equation which involves velocity, distance and acceleration