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## Homework Statement

Susan, driving North at 60 mph, and Shawn, driving East at 45 mph, are approaching an intersection. What is Shawn's speed relative to Susan's reference frame?

## The Attempt at a Solution

The solution is [45^2+60^2]^.5=75mph

.... but I don't really understand why. I do realize that 75 is the hypotenuse of the triangle, I just don't understand how I would have known what this question is asking for, it seems as if there is way too much that the question doesn't tell you. How would I know from looking at this question that it is implied that the vehicles are on a collision course with each other at their exact center of mass?

Any tips for breaking a question down in order to see what it is really asking and implying are appreciated.

I realize that this is kind of a strange question, so any helpful input is appreciated and if it just seems like I'm asking a dumb question, well, I understand that too =)