Question

Can the average speed of a moving object be zero? Can the average velocity of a moving object be zero?justify

Answer 1

Average speed of a moving object can't be zero.

As average speed is defined as the total distance covered with respect to total time taken. If a body is moving with some distance in given time, then there must be a distance travelled by the body.

Average velocity of a moving object can be zero.

Average velocity is defined as the total displacement with respect to the total time taken. Average velocity can be zero if it's initial and final points are same or if there is no distance covered by the object.

$\rule{200}2$

Let's take an example to understand this.

A car travels from A to B at 50 km/hr and return back using the same pathway with a speed of 40 km/hr.

Let us assume that the distance covered by the car is 'x' km.

Since the car starts from A to B, then returns to A point again. So, the distance covered by the car is twice of the distance i.e. 2x km. Also, the initial and final points of the car are same i.e. A point. So, the displacement of the car is 0 km.

Now,

Average speed of defined as the ratio of total distance covered with respect to total time taken.

Time = Distance/Speed

t1 = x/50 hr and t2 = x/40 hr

Total time taken by car = t1 + t2

= x/50 + x/40

= x/10(1/5 + 1/4)

= x/10(9/20)

= 9x/200

Average speed = 2x/(9x/200)

= (2 × 200)/9

= 44.44

Therefore, the average speed of the car is 44.44 km/hr.

Hence, average speed of a moving object can't be zero, but average velocity can be zero.