physics help! conservation of momentum?

Lady Laflin: Sorry if this is a bit long, but I've tried to explain in detail. By the way, they are very light cars; cars are normally around 1000kg! However, we'll ignore this.________________________________________________Say the first car is going in the positive direction.Its initial momentum = mv = 111x9.00 = 999 kgm/s.The second car is going in the opposite (negative) direction; so take v = -5.00m/s.Its initial momentum = mv = 111x(-5.00) = -555 kgm/s.So the total initial momentum = 999 + (-555) = 444 kgm/sThe collision is perectly inelastic, which means the cars stick together. They have a combined mass of 2x111 = 222kg.Say the combined cars have a velocity V after the collision; then the combined cars have momentum = mv = 222V, and this is the final momentum.From conservation of momentum:Initial momentum = final momentum444 = 222VV = 2.00 m/s(Note, the choice of which direction is positive is unimportant. If we had chosen the reverse directions, V would simply! have come out to be -2.00m/s.)________________________________________The 1st car's initial kinetic energy was:½mv² = ½(111)(9.00)² = 4495.5JThe 2nd car's initial kinetic energy was:½mv² = ½(111)(-5.00)² = 1387.5JSo initially, the total kinetic energy = 4495.5 + 1387.5 = 5883JAfter the collision, the combined cars' kinetic energy is:½mv² = ½(222)(2.00)² = 444J.So the kinetic energy has dropped from 5883J to 444J. This is a *change* of 444 - 5883 = -5439J (negative as the kinetic energy has decreased.(The kinetic energy is dissipated â€" i.e. changed to heat.)The value should be rounded to 3 significant figures to match the data supplied in the question. Also, the question asks how much kinetic energy is dissipated â€" not what the change is.The correct answer is 5440J. The answer should not be negative and it should not have been rounded to the nearest 50, so -5450J is incorrect....Show more