Question

A car travels half of the distance with constant velocity of $30\, km/h$ and another half with a constant velocity of $50\, km/h$ along a straight line. The average velocity of the car in $km/h$ is:

• A. 38.7
• B. 42
• C. 37.5
• D. 40

Answer 1

Answer: (C)

A moving bodys average velocity during an interval of time is the total distance covered divided by the total time elapsed while travelling in a given direction.
Let total distance travelled is $x$,
then $V_{av}=\frac{x}{t_{1}+t_{2}}$
Here, $t_{1}=\frac{x/2}{30},\,\,t_{2}=\frac{x/2}{50}$
$\Rightarrow V_{av} =\frac{x}{\frac{x}{30}+\frac{x}{2\times 50}}$
$V_{av}=\frac{2\times 30\times 50}{30+50}$
$=37.5\,km/h$ .