An object travels North at 6 m/s for 4 s and then travels South at 3 m/s for 8 s. What are the object's average speed and velocity?

1 Answer
Dwight
Jan 17, 2017

Its average speed is 4m/s but its average velocity is zero, because at the end of its journey, it is back where it started.

Explanation:

To get the average speed, we need to find the total distance travelled.

d=vxxt

In the first 4s, the distance is 6xx4=24m. In the following 8s, the distance is 3xx8=24m as well.

So, in total, the object has travelled 48 m in 12 seconds

v=d/t = (48m)/(12s) = 4 m/s

(Note that this is not what you would get if you added the two speeds and divided by 2, because the object spends different amounts of time at the different speeds!)

To find average velocity, we need to determine the displacement of the object. Since its first journey was 24 m north, and its second was 24 m south, it has arrived back where it started, for a net displacement of zero.

So, its average velocity is also zero.

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