`S_(1):` If the internal forces within a system are conservative, then the work done by the external forces on the system is equal to the change in mechanical energy of the system.
`S_(2):` The potential energy of a particle moving along `x-` axis in a conservative force field is `U=2x^(2)-5x+1` is `S.I.` units. No other forces are acting on it. It has a stable equalibrium position at one point on `x-` axis.
`S_(3) :`Internal forces can perform net work on a rigid body.
`S_(4) :` Internal forces can perform net work on a non`-` rigid body.