|Class 11 Physics Laws of Motion||Conservation of Momentum|
Conservation of Momentum
Example 1. In a Spinning top, total momentum = 0. For every point, there is another point on the opposite side that cancels its momentum.
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