Define linear momentum and state it's S.I. unit.

A body of mass m moving with a velocity v is acted upon by a force. Write expression for change in momentum in each of the following cases (i) when v << c (ii) when v → c, and (iii) when v << c but m does not remain constant. Here c is the speed of light.

Two balls A and B of masses m and 2m are in motion with velocities 2v and v respectively.
Compare
(i) their inertia, (ii) their momentum, and (iii) the force needed to stop them in same time.

Name the S.I. unit of force and define it.