Vector force magnitude conversion to other direction : <p>I need some help on solving a simple vector force physics question.</p>

<p>Given a force vector (x, y), how to calculate the magnitude of the force apply on the direction (i, j) ?</p>

<p>(For example, given (1, 0) the magnitude of the force apply on the direction (0, 1) should be 0, and given (1, 0) the magnitude of the force apply on the direction (-1, 0) should be -1)</p>

<p>Thank you very much!</p>
