The kinetic energy of any body depends on the frame of reference of the observer. The kinetic energy is given by `1//2 mv_("rel")^(2)`. Similarly the displacement of the object from different frames of reference will be: different. But the forces acting on the body remain unchanged. So work done by the forces as seen from: different frames will be different. But work energy! theorem will still be hold in every inertial reference' frame.
For example, if a block of mass 2kg is moving with, velocity of `1m//s` towards east on a rough surface, its `KE = (1)/(2) xx 2 xx 1^(2) = 1J`
If it comes to rest, its `KE = 0`
work done by friction `= K_(f) - k_(i) = -1 J`
If we observe it form a frame 2 moving with `1m//s` toward east, its initial velocity will appear to be `1 - 1 = 0`
Initial `KE = (1)/(2) xx 2 xx 0^(2) = 0`
Final velocity `= 0 -1 = -1`
Final `KE = (1)/(2) xx 2 xx (-1)^(2) = 1J`
`rArr` Work done by friction `= 1 - 0 = 1J`
Choose correct statement :

Options

A. In ground frame, work done by friction on ground is positive
B. In ground frame, work done by friction on ground is negative
C. In frame 2, work done by friction on ground is negative
D. In frame 2, work done by friction on ground is positive

Answer

C