I believe you are overcomplicating what was probably meant as a simple problem, as well as missing a key point. Look at it this way: The car is device for transforming chemical energy into kinetic energy (with a certain efficiency). We are told that 1 ounce of fuel can be transformed into the KE...
If the truck were in a frictionless world, and the engine of the truck had the same HP at all rpm's, then the energy needed to accelerate 30mp/h would be the same at all speeds. hmmmmm... The rpm's would increase as the truck gained speed, so the amount of fuel used would be greater each...
The momentum of an object is equal to its mass, multiplied by its velocity. The bowling ball will obviously be much heavier than the golf ball, so it will not have as great of a speed, yet because of its mass, would still have about the same momentum. A golf ball would probably bounce back when...