when a body is at rest in an elevation then it has
Answers
Potential energy is not a measurable physical quantity. What can be measured are differences in potential energy. So, if you compare the potential energies of a given mass at the Earth's surface and 100m
100
m
above the surface, you cannot choose their difference, because that is governed by the laws of physics. However, you can freely choose to assign any point in space a specific potential energy (for the mass m
m
). You could define that m
m
's potential energy at the surface is 0
0
, or 1234J
1234
J
, or any other value.
Kinetic energy of a point particle of mass m
m
is defined by mv22
m
v
2
2
, where v
v
is the velocity. "The velocity with respect to what," you may ask. The choice is, again, yours to make; for different frames of references, you get different speeds and kinetic energies, and different notions of "rest". However, as long as m
m
is not accelerating (and m≠0
m
≠
0
), there is always a reference frame in which v=0
v
=
0
and thus Ekin=0
E
kin
=
0
.
So yes, for a body at rest (with regard to an inertial frame) at the surface (or any other point), you could very well claim that it has zero potential and kinetic energy.