Which two controls on a car are primarily responsible for causing a change in $v$?

• A. The clutch and the steering wheel
• B. The accelerator and the brake
• C. The steering wheel and the accelerator
• D. The brake and the gear shift

Answer: (B)

Verified step by step guidance

1. Understand that the variable \( v \) represents the velocity of the car, which depends on both speed and direction.
2. Identify which controls directly affect the speed (magnitude of velocity) of the car: the accelerator increases speed, and the brake decreases speed.
3. Recognize that the steering wheel changes the direction of the car but does not directly change the speed, so it affects the direction component of velocity, not its magnitude.
4. Note that the clutch and gear shift primarily affect how power is transmitted to the wheels but do not directly cause immediate changes in velocity.
5. Conclude that the two controls primarily responsible for causing a change in the velocity \( v \) (specifically its magnitude) are the accelerator and the brake.