Correct! As both cars have stopped, both their speeds are \(0 \, \mathrm{km/h}\). So, the total speed is \(0 + 0 = 0 \, \mathrm{km/h}\). This is obviously \(< 80 \, \mathrm{km/h}\).

Whenever a property doesn't change before and after an event, the property is said to be

But, the total speed before and after a crash is not conserved.

**conserved**. For example, the total number of chocolates is conserved even when you give it to your friends. (Obviously, if someone eats the chocolate, the number is not conserved!)But, the total speed before and after a crash is not conserved.

**Before**the crash, the total speed was \(80 \, \mathrm{km/h}\). After the crash, it is \(0 \, \mathrm{km/h}\). As the total**before**the crash is**different**from the total**after**the crash, we can say that the total speed**isn't conserved**.