When stopping from a higher speed, which factor best explains the need for more friction to stop?

• A. The kinetic energy of the moving mass increases with speed, requiring more friction to stop
• B. The color of the car affects braking
• C. The driver’s eye color changes reaction time
• D. The tires produce less grip at higher temperatures

Answer: (A)

When you stop from a higher speed, more energy has to be removed from the moving mass. The amount of kinetic energy is 1/2 m v^2, which means it grows with the square of speed. Friction between the tires and the road is what converts that energy into heat and slows you down. Because the energy to dissipate is larger at higher speeds, you need more friction (or a longer distance to use up the extra energy) to stop. The other factors—like the car’s color or the driver’s eye color—don’t affect braking physics, and while tire grip can vary with temperature, that doesn’t explain why stopping from a higher speed requires more friction in the same way energy does.