Final answer:
An 18-wheeler has more energy than a bike at the same speed because kinetic energy depends on both mass and velocity, and the truck has a much greater mass.
Step-by-step explanation:
An 18-wheeler has more energy than a bike at the same speed because the kinetic energy (EK) of an object depends not only on its velocity but also on its mass. While both the 18-wheeler and bike may be traveling at 20 mph, the truck's mass is significantly greater. The formula for kinetic energy is EK = 1/2 m v2, where m stands for mass and v for velocity. So for two objects moving at the same velocity, the one with the larger mass will have more kinetic energy. This explains why a huge 18-wheeler would have much more kinetic energy than a relatively lightweight bike at the same speed.