# How can I find the magnitude of a vector B when I know the unit vector B, the vector A and the result cross product of AXB?

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Emmanouil Karamousadakis on 18 Jul 2022
In other words, in a 2D plane, I know the final torque( A X B) on the k (out of the plane), I know the vector A (arm),
I know the direction the B is (the direction of the force) but I do not know the magnitude of that force
I am stuck, any help please?
Thank you!

Torsten on 18 Jul 2022
Calculate
A x B_unit
Then the magnitude of B is
m = norm(A x B)/norm(A x B_unit)
where B_unit is the unit vector in the direction of the force.
Emmanouil Karamousadakis on 18 Jul 2022
Thank you, it worked fine!

### More Answers (1)

Jon on 18 Jul 2022
Lets say you have the final Torque, and arm as a three element vectors T, and A respectiviely. Then I think the magnitude of the force would be
F = norm(T)/norm(A)

R2022a

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