Question

A car covers the first half of the distance between two places at 40 km/h and another half at 60 km/h. The average speed of the car is

• A. 40 km/h
• B. 48 km/h
• C. 50 km/h
• D. 60 km/h

Answer 1

Answer: (B)

Letx consider, $x=$ total distance covered by the car, Time taken to complete the half distance with velocity $v=40km/h$,
$t_1=\frac{x}{2\times 40}=\frac{x}{80}hr\dots ..(1)$
The time taken to complete another half distance with velocity $u=60km/h$
$t_2=\frac{x}{2\times 60}=\frac{x}{120}h$
The total time taken, $t=t_1+t_2$
$t=\frac{x}{80}+\frac{x}{120}=\frac{x}{48}h$
The average speed of the car,
$v_{avg}=\frac{x}{x/48}=48km/h$