Question

A car moving on a straight road covers $1/3$ of the distance with $25\,km/h$ and rest with $75\,km/h$ . The average speed is

• A. $25\,km/h$
• B. $45 \,km/h$
• C. $55\,km/h$
• D. $75\,km/h$

Answer 1

Answer: (B)

$45 \,km/h$

Answer 2

$=V_{a V}=\frac{\text { Total distance covered }}{\text { Total time taken }}$
$=\frac{\frac{x}{3}+\frac{2 x}{3}}{t_{1}+t_{2}}$
[Let the total distance covered is $x\, km$ ]
$=\frac{\frac{x}{3}+\frac{2 x}{3}}{\frac{\left(\frac{x}{3}\right)}{25}+\frac{\left(\frac{2 x}{3}\right)}{75}}$
$=\frac{x}{\frac{x}{75}+\frac{2 x}{225}}=\frac{x}{\frac{(3+2) x}{225}}$
$=\frac{225}{5}=45\, m / s$