The law of conservation of momentum applies to collision problems.
Tips
usage
守恒定律 is the slot you plug a quantity into: 能量守恒定律 (conservation of energy), 动量守恒定律 (momentum), 角动量守恒定律 (angular momentum), 电荷守恒定律 (charge). Standard high-school and college physics terminology.
memory
守 (guard) + 恒 (constant) = 'guard the constant', i.e. the quantity stays unchanged. 定律 = 'law'. So 'guard-constant law' = 'conservation law'.
