Example 2. Bullet fired from a Rifle Initially, momentum = 0
Later, the trigger is pulled, bullet gains momentum in àdirection, but this is cancelled by rifle’ s ß momentum. Therefore, total momentum = 0
During the process, the chemical energy in gunpowder gets converted into heat, sound and chemical energy.
Example3. Rocket propulsion Initially, mass of rocket: M. It just started moving with velocity v Initial momentum = Mv
Later, gases are ejected continuously in opposite direction with a velocity relative to rocket in downward direction giving a forward push to the rocket.
Mass of the rocket becomes( M-m) Velocity of the rocket becomes( v + v’)
Final momentum =( M – m)( v + v’) Thus, Mass * velocity = constant