There are two possible answers:
Velocity gives an idea of how fast the position changes. or Acceleration gives an idea of how fast the velocity changes.

An object moving in uniform circular motion is moving around the perimeter of the circle with a constant speed. While the speed of object is constant, its velocity is changing, Ex: Merry-go-round, roller coaster, planets orbiting the sun.

The centre of gravity of an object is the point through which the entire weight of the object appears to act.

(a) A bus moving with constant speed.

\(\begin{array}{|l|c|c|c|c|c|} \hline \text { Time } & 0 & 1 & 2 & 3 & 4 \\ \hline \text { Distance } & 0 & 10 & 20 & 30 & 40 \\ \hline \end{array}\)
(b) A car parked on road side.

 

\(\begin{array}{|l|c|c|c|c|c|} \hline \text { Time } & 1 & 2 & 3 & 4 & 5 \\ \hline \text { Distance } & 20 & 20 & 20 & 20 & 20 \\ \hline \end{array}\)

Stability:
Stability is a measure of the body's ability to maintain its original position.
The three types of stability are
(i) Stable equilibrium
(ii) Unstable equilibrium
(iii) Neutral equilibrium
Stable Equilibrium:
i) The frustum can be tilted through quite a big angle without toppling.
ii) Its centre of gravity is raised when it is displaced.
iii) The vertical line through its centre of gravity still falls within its base.
iv) So it can return to its original position.


Unstable Equilibrium:
i) The frustum will topple with the slightest tilting. Its centre of gravity is lowered when it is displaced.
ii) The vertical line through its centre of gravity falls outside its base.

Neutral Equilibrium:
(i) It causes frustum to topple.
(ii) The frustum will rolls about but does not topple.
(iii) Its centre of gravity remains at the same height when it is displaced.
(iv) The body will stay in any position to which it has been displaced.

Final velocity (v) = 20 m/s Initial Velocity (u) = 0 m/s.
Time (t) = 10 s
Acceleration (a) =?
\(\text { Acceleration } =\frac{\text { Change in velocity }}{\text { time }} \)
\(=\frac{\text { Final velocity }(\mathrm{v})-\text { Initial velocity }(\mathrm{u})}{\text { time }}=\frac{\mathrm{v}-\mathrm{u}}{\mathrm{t}}=\frac{20-0}{10} \)
Acceleration of the car = 2 m/s².