Easy change in direction question

[rcmango]

Homework Statement

if there's a plane traveling north at 200 m/s and then travel south at 200 m/s then its change in velocity is 400 m/s south.

Homework Equations

The Attempt at a Solution

okay so the answer is 400 m/s south.

however, i don't understand why the change is 400, and not 0 or just 200?

i see the new direction is south.

is there an equation for problems like these?

maybe you could make up another example with the answer included so i can see this better.

thanks.

 

[JasonRox]

Think about it... let's say your traveling 60 miles per hour and then all of the sudden your traveling 20 miles per hour in the same direction? What's the change in velocity? Well, that is 40 miles per hour.

If you're going 60 miles per hour and then you stop all of the sudden, what's the change in velocity?

Now, if you're going 60 miles per hour and then you start going 20 miles per hour in the OPPOSITE direction, what's the CHANGE in velocity?

 

[rcmango]

If you're going 60 miles per hour and then you stop all of the sudden, what's the change in velocity?
...then i would say it is 60 miles per hour, since your not moving anymore. correct?

also,

if you're going 60 miles per hour and then you start going 20 miles per hour in the OPPOSITE direction, what's the CHANGE in velocity?
...i would say 80 miles per hour in the opposite direction because you add them together it seems?

this all seems confusing to me.