Posted by **Mitch** on Saturday, March 6, 2010 at 8:29pm.

ok so dr= 2i + 3j while F= 5i + 2j

It wants me to find the work. now i know w=Fxdr. what i want to know is why when you take the dot product of both, you get a different answer compared to when you just multiply the magnitudes.

- physics -
**drwls**, Saturday, March 6, 2010 at 8:36pm
It is called a dot product, but you typed it like a cross product, which is something else entirely.

The dot product of two vectors is the product of their magnitudes TIMES the cosine of the angle between the vectors. These vectors are not parallel in this case, so the cosine is less than 1.

In your case, the cross product is 16, and the product of the magnitudes is 19.41. The cosine of the angle between the vectors is 0.824. There is a 34.5 degree angle between them.

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