Posted by **Annie** on Sunday, March 17, 2013 at 10:17pm.

A roller coaster cart travelling due north at 20m/s that turns left during an interval of 4.0s without changing speed. Find the average acceleration.

I understand the mathematics behind it (using pythagoras's theorem to find velocity and the formula acceleration = velocity/time) BUT I don't understand how to find the direction.

The answer in my text book says south west, but intuitively that just doesn't make sense if you draw out the path taken. Can anyone explain how the direction is south west?

- Physics -
**Henry**, Monday, March 18, 2013 at 4:41pm
Draw a vector from the origin pointing

due north. Then draw a vector from the

origin pointing due west. Since the 2 vectors are equal, the resultant vector

will fall midway between them(135o or

North West). Mathematically:

tanAr = Y/X = 20/-20 = -1.0

Ar = -45o = Reference angle.

A = -45 + 180 = 135o, North West.

If we change the North bound vector to due South, then the direction would

be South West.

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