The Gravitationa potential energy of the mass (PEG) is given by:
[tex]U=mgh[/tex]
where
m is the mass
g is the gravitational acceleration
h is the heigth of the mass above the reference level (the ground)
In this problem, [tex]m=250 kg[/tex] and [tex]h=0.5 m[/tex], therefore the gravitational potential energy of the mass is:
[tex]U=mgh=(250 kg)(9.8 m/s^2)(0.5 m)=1225 J[/tex]
