Momentum vectors graph ( from aqa paper)

[bonbon22]

Homework Statement

The diagram shows a gas particle about to collide elastically with a wall. box
Which diagram shows the correct change in momentum ∆mv that occurs during the
collision?
https://filestore.aqa.org.uk/sample-papers-and-mark-schemes/2018/june/AQA-74082-QP-JUN18.PDF
question 12 on the multiple choice section
B

Relevant Equations

none

If i were to take one point as my origin and draw the two momentum, one for the initial collestion and one going from the wall after, from the origin point, then drawing horizontally i would get the answer as B as the resultant? Should i assume that for any resultant vector the direction can be found in a similar way ? Just want to make sure my train of thought is correct on this.
the answer is B

 

[stunner5000pt]

I think your answer is correct. If angle of collision with the normal initially is theta. When it bounces back off, it is also theta. We need to move the initial vector to make it negative and we get diagram B