When your'e in space you feel weightless blc there's no grsvity in space.
For free fall motion the displacement can be found by graphically as well as by kinematics equation
Here acceleration of object is constant as it fall due to gravity so we can use

here if body starts with zero initial speed then we can say

here we need to find the displacement from t = 0 to t = 6s
so we can say


so the displacement will be 176.4 m
in order to find the displacement from the graph of velocity and time we need to find the area under the graph for given time interval that will also give us same displacement for given period of time.
I think the answer is thermal energy into electrical energy
Two half lives so it is 4000 years old