Which concept describes how speed and mass influence a vehicle's motion and stopping?

• A. Momentum
• B. Kinetic Energy
• C. Inertia
• D. Friction

Answer: (B)

Kinetic energy describes how speed and mass influence a vehicle’s motion and stopping because it quantifies the amount of energy that must be removed to bring the vehicle to a stop. The energy is given by 1/2 m v^2, so it increases with both mass and the square of speed. This means a faster or heavier vehicle stores more energy, and braking must dissipate that energy as heat to stop. The greater the kinetic energy, the longer the stopping distance or greater the deceleration the brakes must achieve to stop safely.

Inertia is about resisting changes in motion, and momentum is the product of mass and velocity, which relates to how hard it is to change motion but not directly to the energy that must be dissipated during a stop. Friction is the resistive force involved in braking but the concept here focuses on how much energy needs to be removed, which is captured by kinetic energy.