Question

A car is moving on a straight road at a constant speed in a single direction. Which of the following statements is true?

a) Average velocity is zero.

b) The magnitude of average velocity is equal to the average speed.

c) The magnitude of average velocity is greater than the average speed.

d) The magnitude of average velocity is less than the average speed.​

Answer 1

b) The magnitude of average velocity is equal to the average speed.

But why ?

First of all, lets see the definition of average speed and average velocity !

• Average speed is defined as the total distance divided by the total time.

$\boxed{ \bf \: avg. \: speed = \dfrac{total \: distance}{total \: time} }$

• Average velocity is defined as the total displacement divided by the total time.

$\boxed{ \bf \: avg. \: velocity= \dfrac{total \: displacement}{total \: time} }$

Now, when the car is moving on a straight line with a constant velocity, we can say :

• The DISPLACEMENT is equal to DISTANCE.

In that case, average speed is equal to average velocity (option b) ✔️