Question

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

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

Answer 1

Answer: (B)

$=V_{aV}=\frac{\text{ Total distance covered }}{\text{ Total time taken }}$
$=\frac{\frac{x}{3}+\frac{2x}{3}}{t_1+t_2}$
[Let the total distance covered is $xkm$ ]
$=\frac{\frac{x}{3}+\frac{2x}{3}}{\frac{\left(\frac{x}{3}\right)}{25}+\frac{\left(\frac{2x}{3}\right)}{75}}$
$=\frac{x}{\frac{x}{75}+\frac{2x}{225}}=\frac{x}{\frac{(3+2)x}{225}}$
$=\frac{225}{5}=45m/s$