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