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All buses and cars these days are fitted with a speedometer, which shows the velocity of the vehicle. A device called odometer records the distance moved by the vehicle. If the reading on the odometer of a vehicle in the beginning of a trip and after $40$ minutes were $1048\, km$ and $1096\, km$ respectively, calculate its average velocity. Will the reading on the speedometer show this velocity when the vehicle is moving ? Support your answer with reason.
Solution
Average speed is given by
$V _{a v}=\frac{\text { Distance travelled }}{\text { Time taken }}$
The automobile travels a distance of $1096-1048$
$=48 km =48000 m$ in a time $40 min =2400 s$
Therefore, $V _{a v}=\frac{\text { Distance travelled }}{\text { Time taken }}=\frac{48000}{2400}$
$=20\, m s ^{-1}$
The speedometer measures the instantaneous speed and not the average speed, therefore, it will not show this speed.
