$5\mathrm{.}8$ Undertine the correct alternative:

$($a$)$ When a conservattve force docs positive work on a body, the potential energy of the body increases$/$decreases$/$remains unaltered.

$($b$)$ Wark done by a body against friction always results in a loss of its kinetic$/$potential energy.

$($c$)$ The rate of change of total momentum of a many$-$particle system is proportional to the external force$/$sum of the internal forces on the system.

$($d$)$ In an inelastic collision of two bodies, the quantitics which do not change after the collision are the total kinetic energy$/$total linear momentum$/$total energy of the system of two bodies.