A car's speed decreases as the driver brakes. Everyday language calls this "deceleration." How is this correctly described in physics?
AVelocity that remains constant throughout the motion
BAcceleration that points in the same direction as the velocity
CDisplacement that grows increasingly negative with time
DAcceleration whose direction is opposite to the velocity
Answer & Solution
Correct answer: D. Acceleration whose direction is opposite to the velocity
1. In physics, any change in velocity -- whether speeding up, slowing down, or changing direction -- counts as acceleration.
2. When an object slows down, its velocity is decreasing, which means the acceleration vector points opposite to the velocity vector.
3. The text is explicit: "In everyday language, this is called deceleration; but in physics, it is acceleration—whose direction happens to be opposite that of the velocity."
4. So braking is still acceleration in the physics sense -- specifically, acceleration directed opposite to the motion.
_Source: OpenStax Physics Ch 3 "Acceleration", p.99 §3.1 Acceleration_
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