Question

A truck driver drives $20\text{km}$ down the road in $5\text{minutes}$ . He then reverses and drive $12\text{km}$ back down the road in $3\text{minutes}$. What is the average velocity?

• A. $1\text{km/min}$
• B. $2\text{km/min}$
• C. $3\text{km/min}$
• D. $4\text{km/min}$

Answer 1

The correct option is A $1\text{km/min}$

The truck motion can be represented as shown below.
Let truck starts from $A$ and reaches $B$ which is $20\text{km}$ far and then reverse back to reach $C$ by driving $12\text{km}$.
So, net displacement of the truck is $\Delta S=AC=20-12=8\text{km}$
And, total time taken $\Delta t=5+3=8\text{min}$
So, average velocity is given as
$v_{avg}=\frac{△S}{△t}=\frac{8}{8}=1\text{km/min}$