Initial velocity (u) = 0 km/h
Final velocity (v) = 40 km/h
Time (t) = 10 min = \(\frac{10}{60h}=\frac{1}{6h}\)
Acceleration (a) = \(\frac{v-u}{t}=\frac{40-0}{\frac{1}{6}}\) = 40 x 6 = 240 km/h

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

An object undergoes uniform acceleration when the change (increase or decrease) in its velocity for every unit of time is the same.

(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.

 

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

Apparatus: Irregularly shaped plate, string, pendulum bob, stand.
i) Make three holes in the lamina.
ii) Suspend the lamina from the optical pin through one of the holes as shown.
iii) Suspend the plumbline from the pin and mark the position of the plumbline on the lamina.
iv) Draw lines on the lamina representing the positions of the plumbline.
v) Repeat the above steps for the holes.
vi) Label the intersection of the three lines as X is the position of the centre of gravity of the lamina.

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.