Motion describes how the position of an object changes with time. This chapter introduces distance and displacement, speed and velocity, acceleration, the equations of uniformly accelerated motion, and how motion is represented on distance–time and velocity–time graphs.
Can an object that has moved through a distance have zero displacement? Explain with an example.
Yes, it can.
Distance is the total length of the path covered, while displacement is the shortest straight-line distance from the starting point to the final point.
If a body returns to where it started, the initial and final positions are the same, so the displacement is zero even though the path length is not.
Example: an athlete runs one full round of a 400 m circular track. The distance covered is 400 m, but because the finishing point is the starting point, the displacement is 0 m.
Final Answer: Yes — for one complete round of a 400 m track, distance = 400 m but displacement = 0 m.
Common Mistake: Treating distance and displacement as the same quantity.
Exam Tip: Remember: distance is a scalar and is never negative; displacement is a vector and can be zero.
Q2. Question 2 — Uniform Acceleration
A car speeds up uniformly from 18 km/h to 36 km/h in 5 s. Find its acceleration and the distance it covers in this time.
First convert the speeds into m/s:
u = 18 km/h = 18 × 5/18 = 5 m/s
v = 36 km/h = 36 × 5/18 = 10 m/s, and t = 5 s
Acceleration:
a = (v − u)/t = (10 − 5)/5 = 1 m/s²
Distance:
s = ut + ½at² = (5)(5) + ½(1)(5)²
= 25 + 12.5 = 37.5 m
Formula: v = u + at; s = ut + ½at²; 1 km/h = 5/18 m/s
Final Answer: Acceleration = 1 m/s² and distance covered = 37.5 m
Common Mistake: Using km/h directly in the equations of motion without converting to m/s.
Exam Tip: Convert every quantity to SI units before substituting — it prevents most numerical errors.
Q3. Question 3 — Uniform and Non-uniform Motion
Distinguish between uniform and non-uniform motion, giving one example of each.
An object is in uniform motion when it covers equal distances in equal intervals of time, however small those intervals are. Its speed stays constant, so its acceleration is zero.
In non-uniform motion the object covers unequal distances in equal intervals of time, so its speed keeps changing and it has some acceleration.
Example of uniform motion: a car moving steadily at 40 km/h on a straight highway.
Example of non-uniform motion: a car moving through busy traffic, repeatedly speeding up and slowing down.
Final Answer: Uniform motion — equal distances in equal times (zero acceleration); non-uniform motion — unequal distances in equal times (non-zero acceleration).
Common Mistake: Saying uniform motion means the object moves in a straight line only — the key idea is equal distances in equal times.
Exam Tip: Write the definition, then the example — two-mark answers usually expect both.
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