Base on my research is that in order to balance an equation, you need to make sure that both the reactant and the product of the equation is equal. So base on the problem the product has dihydrogen monoxide. So to make sure this equation to be in balanced you need to add coefficients 2 to the oxygen to make it dioxygen on the left side. The balanced equation is now CH4 + 2O2 = CO2 + 2H2O
The 1200 kg car had bo momentum at the initial stage of the journey because it wasn't on motion. But after collision with the 2000 kg car it gained alot of momentum.
