# Average speed of person walking

1. Mar 1, 2013

### babysnatcher

A person walks first at a constant speed of 5.00 m/s along a straight line from point A to point B and then back along the line from B to A at a constant speed of 3.00 m/s. What are (a) her average speed over the entire trip and (b) her average velocity over the entire trip?

I already solved this problem but I think I had to think way outside the box for it so I want to see an easier way to figure this out. For part "(b)", I just wrote as the answer 0 m/s because she ends up in the same spot. I'm not going to talk about "(a)" because I do not want to disrupt peoples problem solving process. I also want to know if it is correct to use 0 m/s rather than 0; I think it is because 0 pressure is not the same as 0 m/s.

Another thing I want to know is why does dividing the sum of the speeds by 2 not work since it is average speed? I think it is because the it took longer travel at 3.0 m/s. And this affects the results because their are two different times to add to eachother.

2. Mar 1, 2013

### cepheid

Staff Emeritus
For part a, average speed is total distance over total time. The key to the problem is just setting the unknown distance between point A and point B as a variable "d". Use the relation distance = speed*time to find the time required to travel each leg of the journey (in terms of d). You will find that this variable d cancels out in the final answer for v.

Yes, physical quantities have dimension, and you must include units when expressing them.