Question

A speeding car travelling at $40km/hr$ decides to slow down to $30km/hr$ after covering half the distance. What is the average speed?

• A. $34.29km/h$
• B. $35.36km/h$
• C. $36.32km/h$
• D. $33.24km/h$

Answer 1

The correct option is A $34.29km/h$

Lets consider $x=$ total distance covered by the car

Half of the distance covered with speed $40km/h$ at time $t_1$

$t_1=\frac{x}{80}hr$

Remaining half distance covered with speed $30km/h$ at time $t_2$

$t_2=\frac{x}{60}hr$

Total time, $t=t_1+t_2$

$t=\frac{x}{80}+\frac{x}{60}=\frac{7x}{240}hr$

Average speed,

$v_{avg}=\frac{Totaldistance}{Totaltime}$

$v_{avg}=\frac{x}{7x/240}=\frac{240}{7}$

$v_{avg}=34.29km/h$

The correct option is A.