Finding displacement from position time graph

[syllll_213]

Homework Statement

For e I am asked to find the displacement of the object, and I could find the total distance travelled (25m + 15m )= 40m and I assumed the direction is the same therefore it will be the displacement for the object. However the answer is -35m and I am unsure why.

Relevant Equations

distance travelled = area under velocity time graph

 

[erobz]

Its displacement is its change in position between over the time interval. Final position ( relative to coordinate frame) minus its initial position relative to coordinate frame. What do you get for that?

 

[syllll_213]

-40?

 

[erobz]

-40?

Yeah, that’s what I get too (meters-don’t forget units). So I suspect an error with the answer key.

 

[kuruman]

. . . I assumed the direction is the same . . .

No such assumption is warranted. Displacement is (final position) - (initial position).

Here, the final position is -15 m and the initial position is +25 m.
So the displacement is (-15 m)-(+25 m) = -40 m.