As we know that in transformers we have

here we know that



now from above equation we will have



It is 6 g/cm3 because density cannot be negative, and it is not speed in which the unit would be m/s.
Answer:
4000J
Explanation:
Given parameters:
Weight of the man = 800N
Height of ladder = 5m
Unknown:
Gravitational potential energy gained = ?
Solution:
The gravitational potential energy is due to the position of a body.
Gravitational potential energy = weight x height
Now insert the parameters;
Gravitational potential energy = 800 x 5 = 4000J