Velocity
Instantaneous Velocity
The speedometer is the car part that indicates the velocity of a car at a given time. The figure shows that the velocity of the car varies. It also shows that, at every instant, the car has a specific velocity. The velocity of a moving body at a particular time is called instantaneous velocity.
To determine instantaneous velocity, a line tangent to the v-t curve at the value of t is drawn. From that straight line, v is determined using the formula.
\[ \text{instantaneous velocity} = \frac{\text{change in distance}}{\text{change in time}} \]or
\[
\begin{aligned}
v &= \frac{\Delta d}{\Delta t}
\end{aligned}
\]
where Δd is the distance or interval between two points of the line, and Δt is the time interval between the two points. Hence, the instantaneous velocity of the car at Δt = 5 s, is
\[ \begin{aligned} &= \frac{200\, \text{km} - 100\, \text{km}}{16\, \text{s} - 11\, \text{s}} \\ &= 20\, \text{m/s} \end{aligned} \]