VIDEO TRANSCRIPT

All of the kinetic energy in this question turns into thermal energy because after the railway cars collide, there's no potential energy and no kinetic energy because they've stopped. So, thermal energy equals the entire change in energy. So that is one half 'mv' squared times two. So this is the kinetic energy of one of the railroad cars and we're going to times that by two because there's two of them. That’s the total kinetic and the change in kinetic energy'll be that minus the final kinetic energy but there is no final kinetic energy so we can leave it like that.

So the thermal energy is 'mv' squared because the one half and the two cancel. So we got 7,650 kilograms times 95 kilometers per hour divide by 3.6 to make meters per second and square that. We get 5.3 times 10 to the six joules. In the fifth edition, the weight of the railroad car is 6,500 kilograms, so the fifth edition answer is 4.5 times 10 to the six joules.