For two physics students to measure the same velocity of a car, they must be in what?

To measure the same velocity of a car, two physics students must be in the same reference frame. A reference frame is essentially a viewpoint from which measurements are made and can be thought of as a coordinate system. When two observers are in the same reference frame, they are using the same physical principles and conditions to evaluate the motion of the car, meaning they will obtain identical results for the car's velocity.

If the students were in different reference frames, the measurements could vary significantly due to differences in their relative motion. For example, if one student is in a moving vehicle and the other is stationary, they will perceive the car's velocity differently based on their own motion relative to the car. Hence, observing the same velocity requires that both students share the same reference frame in order to ensure consistent measurements.

The other options suggest conditions that would lead to varying measurements of the car's velocity, either due to relative motion (different reference frame) or the influence of acceleration (stationary or accelerated reference frames), which could cause discrepancies in the observed velocity. Thus, being in the same reference frame is essential for consistency in the measurement of velocity.