Physics · Motion In A Straight Line · NEET
Yes. Average speed uses total distance (path length) and average velocity uses displacement (straight-line gap from start to end). Distance is always greater than or equal to |displacement|, and both are divided by the same time. So average speed >= |average velocity| always. They become equal only when the motion is along a straight line without changing direction, so distance equals displacement.
Yes, and this is a favourite NEET point. If a body returns to its starting position, its displacement is zero, so average velocity = 0 / t = 0. But it still travelled a real path, so total distance is not zero, making average speed positive. Example: run 100 m and come back in 40 s. Average velocity = 0 m/s, average speed = 200 / 40 = 5 m/s.
Only when the object moves in a straight line and does not reverse direction (no turning back). Then the path length equals the displacement magnitude, so the two averages are equal in size. The moment the object turns around even once, distance exceeds displacement and average speed becomes larger.
Average speed is a scalar. It has only a value, no direction, and is never negative. Average velocity is a vector. It has a value and a direction, and it can be positive, negative, or zero depending on the sign convention you choose for the displacement.
Yes. Both use the total time for the whole journey, including any stops or pauses. The only difference is the top of the fraction: total distance for average speed, and displacement for average velocity. Never mix a partial time with a total distance.
A toy car with charge q moves on a frictionless horizontal plane under a uniform electric field E. Due to the force qE its velocity increases from 0 to 6 m/s in one second. At that instant the field is reversed. The car moves for two more seconds under this field. The average velocity and the average speed of the car from t = 0 to t = 3 s are respectively:
A particle moves along a straight line with position s(t) = alpha t^2 - beta t + gamma, where alpha = 1 m/s^2, beta = 6 m/s and gamma = 5 m. The average speed of the particle (in m/s) from t = 0 to t = 6 s is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Average speed = total distance / total time and is a scalar that is never negative. Average velocity = total displacement / total time and is a vector that can be positive, negative, or zero. Distance counts the whole path; displacement counts only the straight gap from start to end.
Yes, but only when the object moves in a straight line without turning back. Then distance equals the magnitude of displacement, so the two averages match in size. In any journey with a change of direction, average speed is larger.
NEET regularly asks numericals where a body reverses direction or completes a round trip. Students who blindly average the speeds get it wrong. Knowing that speed uses distance and velocity uses displacement lets you score these questions quickly and avoid the common trap.
Velocity and vector both start with a similar idea of direction, so velocity uses displacement (the directional quantity). Speed is a plain scalar, so it uses distance (the plain path length). Speed = distance, Velocity = displacement.
