Help mechanics

I don’t get why the average velocity is -1
For part e
Isn’t it the displacement over time which is

For the top of graph area is 5000
And then bottom is 400
So when I do 5000-400 I get 4600 which isn’t correct plz help and explain

(edited 11 months ago)

Reply 1

TravelMasterA

The correct answer is actually mentioned in the image - the displacement at t = 80s is -80m, so average velocity is total displacement over time, ie -80/80 = -1 m/s^2
This is not a v-t graph, but an s-t graph, so we do not find the area of the graph to find displacement. Instead, the displacement is given to you in the axes. You can try think of the situation as follows:
Bob travels at constant velocity for 20s until 100m, then stops for 30s, then walks in the opposite direction and reaches the origin at t = 70s, then walks to 80m beyond the origin in the opposite direction.
Does this help?

(edited 11 months ago)