Momentum

p = m \cdot v
\text{momentum} = \text{mass} \cdot \text{velocity}

[!def]
quantity possessed by masses in motion
measure of how difficult it is to stop something that is moving

Collision

conservation of momentum (动量守恒)

m_{1}v_{1}+m_{2}v_{2} = m_{1}u_{1}+m_{2}u_{2}

Elastic collision

No energy lost, collision in noble gas or ideal gas

Partially elastic collision

Inelastic collision

Explosion

Change in momentum

\frac{\Delta p}{t} = F, \text{where } \Delta p \text{ is Impluse}
I = Ft, \ F=\frac{\Delta p}{t} = \frac{m\Delta v}{t} = ma
p=m_{1}v_{1}+m_{2}v_{2}=0.5\times 20 + 0 = 10\ m\cdot kg\cdot s^{-1}
p_{a}=0.5\times-5 = -2.5
p_{b} = p-p_{a} = 10+2.5=12.5
v_{b}=\frac{p_{b}}{m_{b}}=\frac{12.5}{8}=1.56\ m\cdot s^{-1}