Posted by Jessica on .
A sedan weighing 4000 pounds travelling at 30mph collides head on with a compact car weighing 2000 pounds and travelling in the opposite direction at 45 mph. What is the resultant velocity of the combined vehicles?

Physical Science 
drwls,
Assume that the two cars stick together and appply that law of conservation of momentum.
4000*30 2000*45 = 6000*Vfinal
Vfinal = (1.2*10^5  0.9*10^5)/6000
= 5.0 mph (in the original drection of the 4000 lb car).
I did not have to convert mass to slugs or velocities to ft/sec, because I used the same units for each term (lbmass*miles/h)